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.

[patterns]
**.h = native
**.c = native
**.cpp = native
**.lua = native
**.txt = native
**.pas = native
**.inc = native
**.hs = native