Don't leak blocks if GetCheckedHandle throws.

src/Network/NWConnection.cs

@@ -109,10 +109,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_stateChangeHandler, stateHandler);
 
+				try {
 					nw_connection_set_state_changed_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate void nw_connection_boolean_event_handler_t (IntPtr block, [MarshalAs(UnmanagedType.U1)] bool value);
 		static nw_connection_boolean_event_handler_t static_BooleanChangeHandler = TrampolineBooleanChangeHandler;
@@ -141,10 +144,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_BooleanChangeHandler, callback);
 
+				try {
 					nw_connection_set_viability_changed_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[DllImport (Constants.NetworkLibrary)]
 		static extern unsafe void nw_connection_set_better_path_available_handler (IntPtr handle, void *callback);
@@ -162,10 +168,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_BooleanChangeHandler, callback);
 
+				try {
 					nw_connection_set_better_path_available_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate void nw_connection_path_event_handler_t (IntPtr block, IntPtr path);
 		static nw_connection_path_event_handler_t static_PathChanged = TrampolinePathChanged;
@@ -191,10 +200,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_PathChanged, callback);
 
+				try {
 					nw_connection_set_path_changed_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[DllImport (Constants.NetworkLibrary)]
 		static extern void nw_connection_set_queue (IntPtr handle, IntPtr queue);
@@ -302,10 +314,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ReceiveCompletion, callback);
 
+				try {
 					nw_connection_receive (GetCheckedHandle (), minimumIncompleteLength, maximumLength, (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[BindingImpl (BindingImplOptions.Optimizable)]
 		public void ReceiveData (uint minimumIncompleteLength, uint maximumLength, NWConnectionReceiveDispatchDataCompletion callback)
@@ -318,10 +333,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ReceiveCompletionDispatchData, callback);
 
+				try {
 					nw_connection_receive (GetCheckedHandle (), minimumIncompleteLength, maximumLength, (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[DllImport (Constants.NetworkLibrary)]
 		static extern unsafe void nw_connection_receive_message (IntPtr handle, void *callback);
@@ -337,10 +355,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ReceiveCompletion, callback);
 
+				try {
 					nw_connection_receive_message (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[BindingImpl (BindingImplOptions.Optimizable)]
 		public void ReceiveMessageData (NWConnectionReceiveDispatchDataCompletion callback)
@@ -353,10 +374,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ReceiveCompletionDispatchData, callback);
 
+				try {
 					nw_connection_receive_message (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate void nw_connection_send_completion_t (IntPtr block, IntPtr error);
 		static nw_connection_send_completion_t static_SendCompletion = TrampolineSendCompletion;
@@ -424,10 +448,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_SendCompletion, callback);
 
+				try {
 					LowLevelSend (GetCheckedHandle (), buffer, context.Handle, isComplete, block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		static IntPtr _nw_connection_send_idempotent_content;
 

src/Network/NWContentContext.cs

@@ -182,10 +182,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ProtocolIterator, callback);
 
+				try {
 					nw_content_context_foreach_protocol_metadata (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		//
 		// Use this as a parameter to NWConnection.Send's with all the default properties

src/Network/NWListener.cs

@@ -133,10 +133,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_ListenerStateChanged, callback);
 
+				try {
 					nw_listener_set_state_changed_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate void nw_listener_new_connection_handler_t (IntPtr block, IntPtr connection);
 		static nw_listener_new_connection_handler_t static_NewConnection = TrampolineNewConnection;
@@ -167,10 +170,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_NewConnection, callback);
 
+				try {
 					nw_listener_set_new_connection_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate void nw_listener_advertised_endpoint_changed_handler_t (IntPtr block, IntPtr endpoint, byte added);
 		static nw_listener_advertised_endpoint_changed_handler_t static_AdvertisedEndpointChangedHandler = TrampolineAdvertisedEndpointChangedHandler;
@@ -204,10 +210,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_AdvertisedEndpointChangedHandler, callback);
 
+				try {
 					nw_listener_set_advertised_endpoint_changed_handler (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[DllImport (Constants.NetworkLibrary)]
 		extern static void nw_listener_set_advertise_descriptor (IntPtr handle, IntPtr advertiseDescriptor);

src/Network/NWParameters.cs

@@ -377,10 +377,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_iterateProhibitedHandler, iterationCallback);
 
+				try {
 					nw_parameters_iterate_prohibited_interfaces (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		delegate bool nw_parameters_iterate_interface_types_block_t (IntPtr block, NWInterfaceType type);
 		static nw_parameters_iterate_interface_types_block_t static_IterateProhibitedTypeHandler = TrampolineIterateProhibitedTypeHandler;
@@ -408,10 +411,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_IterateProhibitedTypeHandler, callback);
 
+				try {
 					nw_parameters_iterate_prohibited_interface_types (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[TV (12,0), Mac (10,14), iOS (12,0)]
 		[DllImport (Constants.NetworkLibrary)]

src/Network/NWPath.cs

@@ -121,9 +121,12 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_Enumerator, callback);
 
+				try {
 					nw_path_enumerate_interfaces (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
 		}
+	}
 }

src/Network/NWProtocolStack.cs

@@ -71,10 +71,13 @@ namespace Network {
 				BlockLiteral *block_ptr_handler = &block_handler;
 				block_handler.SetupBlockUnsafe (static_iterateHandler, callback);
 
+				try {
 					nw_protocol_stack_iterate_application_protocols (GetCheckedHandle (), (void*) block_ptr_handler);
+				} finally {
 					block_handler.CleanupBlock ();
 				}
 			}
+		}
 
 		[TV (12, 0), Mac (10, 14), iOS (12, 0)]
 		[DllImport (Constants.NetworkLibrary)]