Switch the layout activity to true before actually displaying the layout. This
gives controls a chance to reinitialize before any real drawing occurs, and
thus a clean animation gets displayed without any unwanted stray image.

This fixes trac #12083

(cherry picked from commit 1ce3c5d673ba7a71f3db5cf7f1d11ee906f92d39)
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>