backend/drm: Exit-early if 0 crtcs
This fixes an assertion failure if we're using a device that has 0 crtcs
as a renderer.
This would happen on some laptops with discrete GPUs.
@@ -1140,6 +1140,14 @@ static uint32_t get_possible_crtcs(int fd, drmModeRes *res,
}
void scan_drm_connectors(struct wlr_drm_backend *drm) {
+ /*
+ * This GPU is not really a modesetting device.
+ * It's just being used as a renderer.
+ */
+ if (drm->num_crtcs == 0) {
+ return;
+ }
+
wlr_log(WLR_INFO, "Scanning DRM connectors");
drmModeRes *res = drmModeGetResources(drm->fd);
