Explicity check the last entry in the DB and make sure that we don't iterate
past it. Since there can be no duplicates, this just makes sure that we stop
after matching the last key.
This patch also refactors the code to get away from some code duplication. A
previous patch added many astdb tests and this patch passed them.
Review: https://reviewboard.asterisk.org/r/1259/
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@322981 65c4cc65-6c06-0410-ace0-fbb531ad65f3