gpu-kms: Don't crash if drmModeGetResources returns NULL

gpu-kms: Don't crash if drmModeGetResources returns NULL

DRM drivers can be opened by meta_launcher_open_restricted() even if they don't
implement modesetting. However, drmModeGetResources() will return NULL.

Check whether that happened in meta_gpu_kms_new() and return with an error
instead of crashing.

Fixes #223.

Applied-Upstream: https://gitlab.gnome.org/GNOME/mutter/commit/62660bbd15
Bug-GNOME: https://gitlab.gnome.org/GNOME/mutter/issues/223
Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1767956

Gbp-Pq: Name gpu-kms-Don-t-crash-if-drmModeGetResources-returns-N.patch