Fixing Tag view if core_access is not set

3rd party extension may have tagged items without an access column. Those are saved into #__ucm_content with access = 0.
Currently they show in the similar tag module, but not in the tag view.

This PR fixes this.

Tracker:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30588