rem: if ( listbutton )
add: if ( listbutton && GTK_IS_WIDGET(listbutton) )
context: gboolean gtk_list_button_clicked ( GtkButton *button ){  GtkListButton * listbutton;  GtkWidget * old, * new;  listbutton = groups [ GTK_LIST_BUTTON(button) -> group ];  if ( listbutton )    {      gtk_widget_hide ( listbutton -> open_icon );      gtk_widget_show ( listbutton -> closed_icon );      g_object_ref ( listbutton -> open_icon );      gtk_container_add ( GTK_CONTAINER (listbutton -> box), 			  listbutton -> closed_icon );      gtk_container_remove ( GTK_CONTAINER (listbutton -> box), 			     listbutton -> open_icon );    }  listbutton = GTK_LIST_BUTTON(button);  gtk_widget_hide ( listbutton -> closed_icon );  gtk_widget_show ( listbutton -> open_icon );  g_object_ref ( listbutton -> closed_icon );  gtk_container_add ( GTK_CONTAINER (listbutton -> box), 		      listbutton -> open_icon );  gtk_container_remove ( GTK_CONTAINER (listbutton -> box), 			 listbutton -> closed_icon );  groups [ GTK_LIST_BUTTON(button) -> group ] = listbutton;  return FALSE;}