If, for instance, video is not embedded and visible="vlc.hasVout" is used
for a video control, the video control background was not refreshed.
Yet, partial redraw (overlapping windows) could occur, leading to a visual artefact.
(cherry picked from commit a8fcb7dd6c253e8534d8582b4ef2f9ba30fae691)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>