rootston: server backend check

rootston/main.c

@@ -31,9 +31,9 @@ int main(int argc, char **argv) {
 	assert(server.wl_display = wl_display_create());
 	assert(server.wl_event_loop = wl_display_get_event_loop(server.wl_display));
 
-	assert(server.backend = wlr_backend_autocreate(server.wl_display));
+	server.backend = wlr_backend_autocreate(server.wl_display);
 
-	if (wlr_multi_is_empty(server.backend)) {
+	if (server.backend == NULL) {
 		wlr_log(L_ERROR, "could not start backend");
 		wlr_backend_destroy(server.backend);
 		return 1;