GtkRecentChooserMenu: avoid accessing a NULL action

When the GtkActivatable sets the related action, the activatable
properties are sync'ed. In this case the null check is important
to avoid updating from a NULL action.

gtk/gtkrecentchoosermenu.c

@@ -1202,6 +1202,9 @@ static void
 gtk_recent_chooser_sync_action_properties (GtkActivatable *activatable,
 				           GtkAction      *action)
 {
+  if (!action)
+    return;
+
   gtk_widget_set_sensitive (GTK_WIDGET (activatable), gtk_action_is_sensitive (action));
 
   _gtk_recent_chooser_sync_action_properties (activatable, action);