xwayland: check `glamor_set_pixmap_texture()` status

With `glamor_set_pixmap_texture()` returning its status, remove the hack
and use the return value.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
3 jobs for issue661 in 5 minutes and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #322537
debian-testing

00:00:31

 
  Build And Test
passed #322538
autotools-build-and-test

00:05:09

passed #322539
meson-build-and-test

00:01:26