compositor-wayland: Check the return value of wayland_output_create_common

If wayland_output_create_common returns NULL, it means that
the output creation failed.

Signed-off-by: Sergi Granell <xerpi.g.12@gmail.com>
Reviewed-by: Armin Krezović <krezovic.armin@gmail.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
1 file changed