Avoided triggering an assertion when focus is returned by a popup menu to a hidden component

modules/juce_gui_basics/menus/juce_PopupMenu.cpp

@@ -1621,7 +1621,7 @@ struct PopupMenuCompletionCallback  : public ModalComponentManager::Callback
             if (prevTopLevel != nullptr)
                 prevTopLevel->toFront (true);
 
-            if (prevFocused != nullptr)
+            if (prevFocused != nullptr && prevFocused->isShowing())
                 prevFocused->grabKeyboardFocus();
         }
     }