xwm_get_render_format: check NULL return value

xwayland/xwm.c

@@ -1254,6 +1254,10 @@ static void xwm_get_render_format(struct wlr_xwm *xwm) {
 		xcb_render_query_pict_formats(xwm->xcb_conn);
 	xcb_render_query_pict_formats_reply_t *reply =
 		xcb_render_query_pict_formats_reply(xwm->xcb_conn, cookie, NULL);
+	if (!reply) {
+		wlr_log(L_ERROR, "Did not get any reply from xcb_rrender_query_pict_formats");
+		return;
+	}
 	xcb_render_pictforminfo_iterator_t iter =
 		xcb_render_query_pict_formats_formats_iterator(reply);
 	xcb_render_pictforminfo_t *format = NULL;