xwm: Fix crash when we don't have a transient_for window
diff --git a/src/xwayland/window-manager.c b/src/xwayland/window-manager.c
index da4a4af..ac72458 100644
--- a/src/xwayland/window-manager.c
+++ b/src/xwayland/window-manager.c
@@ -1323,7 +1323,7 @@
 						      &shell_client);
 
 	/* ICCCM 4.1.1 */
-	if (!window->override_redirect) {
+	if (!window->override_redirect || !window->transient_for) {
 		shell_interface->set_toplevel(window->shsurf);
 		return;
 	}