native: Return an error if no drm devices are found

Without this, we'll end up segfaulting when trying to log the
non-existing error.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1217

src/backends/native/meta-udev.c

@@ -148,6 +148,13 @@ meta_udev_list_drm_devices (MetaUdev  *udev,
       l = l_next;
     }
 
+  if (!devices)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "No DRM devices found");
+      return NULL;
+    }
+
   return devices;
 }