Correction to work with gatekeeper which don't send GK ID

Don't use GK ID if it's not presented in GK replies
Extract GK ID not only in GK confirm but in GK register confirm also

(closes issue #18401)
Reported by: MrHanMan
Patches:
      no-gkid-2.patch uploaded by may213 (license 454)
Tested by: may213, MrHanMan



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@298100 65c4cc65-6c06-0410-ace0-fbb531ad65f3