Labels are sometimes (most of the time?) NULL for extensions.

(closes issue #14895)
 Reported by: chris-mac
 Patches: 
       20090423__bug14895__2.diff.txt uploaded by tilghman (license 14)
 Tested by: lmadsen


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@190352 65c4cc65-6c06-0410-ace0-fbb531ad65f3