This cleans up the duplication in fbChangeWindowAttributes,
and fixes a bug if the fb24_32ReformatTile ever failed,
since the old code would happily dereference it in the fbEvenTile
call a few lines later.
Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>