cdr_pgsql does not detect when a table is found.

This change adds an ERROR message to let you know when a failure exists to
get the columns from the pgsql database, which typically means that the
table does not exist.

(closes issue #17478)
Reported by: kobaz
Patches:
      cdr_pgsql.patch uploaded by kobaz (license 834)
Tested by: kobaz, russell, lmadsen

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@275626 65c4cc65-6c06-0410-ace0-fbb531ad65f3