QTfrontend: Fix flickering and bad offset of control config popup
If you opened the pop-up to change a key, there was a very short flicker at the left side
and the pop-up had a bad offset which sometimes caused entries to be out of screen bounds.
AAAAw3icJc6xDcIwEAXQz+niWBhkiggxAS0djZs0kYVASFmBBWiYw0xAQ5sOV7SZgBpKRvAC+Ezz9PWlfzrd8BHmyzvwiTvoFe7QTf0AAoaIUO9hrwUMpQN56iN5tcT8U6C+dKADuzi7scsHeJuEnCaXJOSkXklAtWaXBBjDbRJKF/7dgtsgyPYcBNm+gwBtaTNqqzyqJ3fj1Oeff4W8JYk=