qt: update forgotten emit to Q_EMIT in macdockiconhandler.mm

Leftover from #6433

src/qt/macdockiconhandler.mm

@@ -130,5 +130,5 @@ void MacDockIconHandler::handleDockIconClickEvent()
         this->mainWindow->show();
     }
 
-    emit this->dockIconClicked();
+    Q_EMIT this->dockIconClicked();
 }