fix subscription issue on OnError and OnDone

com.unity.uiwidgets/Runtime/async/stream_impl.cs

         public override void onError(Action<object, string> handleError) {
             handleError = handleError ?? ((input1, input2) => _stream._nullErrorHandler(null));
 
-            _onError = (_, __) => _zone
+            _onError = (arg1, arg2) => _zone
-                });
+                }).Invoke(arg1, arg2);
         }
 
         public override void onDone(Action handleDone) {
                 return null;
-            });
+            }).Invoke();
         }
 
         public override void pause(Future resumeSignal) {