fix: flushing send and receive queues upon disconnection (#2274)

com.unity.netcode.gameobjects/Runtime/Core/NetworkManager.cs

@@ -1341,6 +1341,7 @@ namespace Unity.Netcode
         private void DisconnectRemoteClient(ulong clientId)
         {
             var transportId = ClientIdToTransportId(clientId);
+            MessagingSystem.ProcessSendQueues();
             NetworkConfig.NetworkTransport.DisconnectRemoteClient(transportId);
         }
 
@@ -1821,6 +1822,10 @@ namespace Unity.Netcode
                         NetworkLog.LogInfo($"Disconnect Event From {clientId}");
                     }
 
+                    // Process the incoming message queue so that we get everything from the server disconnecting us
+                    // or, if we are the server, so we got everything from that client.
+                    MessagingSystem.ProcessIncomingMessageQueue();
+
                     OnClientDisconnectCallback?.Invoke(clientId);
 
                     if (IsServer)