[Bugfix]Gui: allow set up expression even if property value is currently being edited

src/Gui/propertyeditor/PropertyEditor.cpp

@@ -748,6 +748,7 @@ void PropertyEditor::contextMenuEvent(QContextMenuEvent *) {
     case MA_Expression:
         if(contextIndex == currentIndex()) {
             Base::FlagToggler<> flag(binding);
+            closeEditor();
             openEditor(contextIndex);
         }
         break;