Start rtp on answer before the answer is queued

(closes issue #17770)
Reported by: salecha
Patches:
      skinny.answercrash.diff uploaded by wedhorn (license 30)
Tested by: salecha

Review: NA 


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@281226 65c4cc65-6c06-0410-ace0-fbb531ad65f3