reset ContextMenu whose popup cannot be opened (#5843)

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/Popup.cs

@@ -1490,6 +1490,12 @@ private void CreateWindow(bool asyncCall)
                     // We'll defer until later if not already in an async call.
                     _asyncCreate = Dispatcher.BeginInvoke(DispatcherPriority.Input, new DispatcherOperationCallback(AsyncCreateWindow), this);
                 }
+                else
+                {
+                    // if the target is still not hooked up in the async call, the popup cannot
+                    // be opened;  raise the CouldClosed event, to inform the original caller
+                    FirePopupCouldClose();
+                }
 
                 return;
             }