Don't pass zero length callerid to ooh323 stack

Don't pass zero length callerid to ooh323 stack

Don't pass zero callerid string to ooh323 stack because it can't encode this properly and
can't generate setup message.

(closes issue #17186)
Reported by: vmikhelson
Patches:
      zero_callerid_num.patch uploaded by may213 (license 454)
Tested by: may213

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@258838 65c4cc65-6c06-0410-ace0-fbb531ad65f3