Prevent crashes from occurring due to a strcmp of a NULL pointer.

(closes issue #12661)
Reported by: jaroth
Patches:
      urgentcompare.patch uploaded by jaroth (license 50)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@116590 65c4cc65-6c06-0410-ace0-fbb531ad65f3