If down or over images are missing, they default to the up image. Yet, in case
of animated images, the animation gets played leading to undesirable artefacts.

This patch adds a comparison operator for animated images and do not restart the
animation if they are alike.

(cherry picked from commit 1c101b97678e5e7a34a062916b24fe0b9366a316)
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>