[#33976] Fix error COM_CONTACT_ERROR_UNIQUE_ALIAS

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33976&start=0
Merge pull request #4021 from illovo/patch-6

[#33976] [2.5] Fix error COM_CONTACT_ERROR_UNIQUE_ALIAS