compositor-drm: Prevent a crash in the pixman renderer
compositor-drm: Prevent a crash in the pixman renderer

When pixman is used and no connector could be found (or any other
error), drm_backend_create() tried to destroy a gbm_device that would
only be created in init_egl(), resulting in a segfault.

Signed-off-by: Emmanuel Gil Peyrot <c5bfa8073b60edb11901ba5bb7dfd0306311c8be@collabora.com>
Reviewed-by: Quentin Glidic <241385a0e41ea713327e189bce1062decf7c1eb5@sardemff7.net>
Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

giucam/weston,giucam/weston,krezovic/weston,Gnurou/weston,Gnurou/weston,krezovic/weston,sir-murray/weston,sir-murray/weston