kms/impl-device/simple: Avoid destroying a NULL hash table
Which would trigger:
g_hash_table_destroy: assertion 'hash_table != NULL' failed
on non-KMS systems like with nvidia-drm.modeset=0
.
Which would trigger:
g_hash_table_destroy: assertion 'hash_table != NULL' failed
on non-KMS systems like with nvidia-drm.modeset=0
.