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 7 minutes and 39 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #187151
debian-testing

00:00:38

 
  Build And Test
passed #187152
autotools-build-and-test

00:07:00

passed #187153
meson-build-and-test

00:01:23