[registrar] Don't let a failure to copy back a parameter go unnoticed.

Now that we ignore parameters we're not copying back, we can throw an
exception if we run into a parameter we don't know how to copy back.

runtime/trampolines-invoke.m

@@ -611,6 +611,9 @@ xamarin_invoke_trampoline (enum TrampolineType type, id self, SEL sel, iterator_
 					goto exception_handling;
 				}
 				*(NSObject **) arg = obj;
+			} else {
+				exception_gchandle = xamarin_get_exception_for_parameter (8030, 0, "Unable to marshal the out/ref parameter", sel, method, p, i, false);
+				goto exception_handling;
 			}
 		}
 		iterator (IteratorEnd, context, NULL, 0, NULL, &exception_gchandle);