PHP notice when looking up item type

This type of look-up may cause notices when no item types have been configured:

$item_type = t($config['editability']['item_types'][$depth]);
$item_type = (!empty($item_type)) ? $item_type : t('item');

This snippet occurs *six* times in hierarchical_select.module, both in D7 and D6, sometimes with slightly different parameters. Let's fix it.