PHP 5.3 Notice: Undefined property: stdClass::$title_label in node_type_save()

When running drush updb on a PHP 5.3 install of Drupal 6, node_type_save is invoked with a node type to save.

It's possible for many of the fields in this node type to be empty, such as title_label. CCK doesn't require them on the input form and it doesn't cause any issues not to have them there, so I think node.module shouldn't throw Notice errors when they aren't set.

This patch suppresses errors when trying to access what I believe to be all the non-required and non-computed fields in this function - no behaviour change at all, just quieting this down so any big errors can be spotted in the logs.