Fix for Postgres driver: Missing column info causes fatal error

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33464&start=0
Fix for unit tests
Fix
Adapted unit test as well.
Merge pull request #3293 from vdespa/patch-6

[#33464] Fix for Postgres driver: Missing column info causes fatal error