Ensure that TabWidget was not deleted by using it as context object (#612)

Co-authored-by: Marcus Venturi <marcus.venturi@visu-it.de>

Author: UnlimitedStack

src/DockAreaTabBar.cpp

@@ -111,8 +111,9 @@ void DockAreaTabBarPrivate::updateTabs()
 			// Sometimes the synchronous calculation of the rectangular area fails
 			// Therefore we use QTimer::singleShot here to execute the call
 			// within the event loop - see #520
-			QTimer::singleShot(0, [&, TabWidget]{
-			    _this->ensureWidgetVisible(TabWidget);
+			QTimer::singleShot(0, TabWidget, [&, TabWidget]
+			{
+				_this->ensureWidgetVisible(TabWidget);
 			});
 		}
 		else