layout manager: add a check if the widget exists

Avoid a crash when calling _gtk_widget_get_first_child
Fixes https://github.com/gtk-rs/gtk4-rs/issues/889

diff --git a/gtk/gtklayoutmanager.c b/gtk/gtklayoutmanager.c
index 57746fd03e316875411860c06a562e56158305fd..6467b8ee5a881e7d91b4db22f2fcf1dd118585dc 100644 (file)
--- a/gtk/gtklayoutmanager.c
+++ b/gtk/gtklayoutmanager.c
@@ -424,6 +424,7 @@ gtk_layout_manager_get_request_mode (GtkLayoutManager *manager)
   GtkLayoutManagerClass *klass;
 
   g_return_val_if_fail (GTK_IS_LAYOUT_MANAGER (manager), GTK_SIZE_REQUEST_CONSTANT_SIZE);
+  g_return_val_if_fail (priv->widget != NULL, GTK_SIZE_REQUEST_CONSTANT_SIZE);
 
   klass = GTK_LAYOUT_MANAGER_GET_CLASS (manager);