Qt: fix focus on GotoTime dismiss

Close #7914
returns highlight focus to main window on Go/Cancel/[Esc] in GotoTime dialogue
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/dialogs/gototime.cpp

@@ -92,7 +92,8 @@ void GotoTimeDialog::toggleVisible()
         timeEdit->setTime( timeEdit->time().addSecs( i_time / 1000000 ) );
     }
     QVLCDialog::toggleVisible();
-    activateWindow ();
+    if(isVisible())
+        activateWindow();
 }
 
 void GotoTimeDialog::cancel()