The compositor crashes when a window does:
has shadow -> no shadow -> has shadow
This is because when the shadow is turned off, the shadow image is not
freed, and this is catched by a later assertion.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
If a window is unmapped during the draw_callback re-run when the screen
is just redirected, that window won't get a chance to acquire a pixmap.
If fading is enabled, the compositor will try to render that window and
crash.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
