listitemfactory: Don't rebind on position or selection changes

When the item doesn't change and only the position / selection state,
then the signal list item factory should not emit bind + unbind signals.

This used to work, but probably broke while refactoring for ColumnView
during 4.10.

This caused excessive rebinding when items got inserted at the top of a
list instead of add the end.

gtk/gtklistfactorywidget.c

@@ -191,10 +191,12 @@ gtk_list_factory_widget_update (GtkListItemBase *base,
 
   if (priv->object)
     {
+      gpointer old_item = gtk_list_item_base_get_item (GTK_LIST_ITEM_BASE (self));
+
       gtk_list_item_factory_update (priv->factory,
                                     priv->object,
-                                    gtk_list_item_base_get_item (GTK_LIST_ITEM_BASE (self)) != NULL,
-                                    item != NULL,
+                                    item != old_item && old_item != NULL,
+                                    item != old_item && item != NULL,
                                     gtk_list_factory_widget_update_func,
                                     &update);
     }