Don't override a user option with the global option.

(closes issue #16849)
 Reported by: ip-rob
 Patches: 
       20100311__issue16849.diff.txt uploaded by tilghman (license 14)
 Tested by: ip-rob


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@251989 65c4cc65-6c06-0410-ace0-fbb531ad65f3