originate/call forwarding: Fix a crash when forwarding a call from originate

(closes issue ASTERISK-22487)
Reported by: David M. Lee
Review: https://reviewboard.asterisk.org/r/2868/
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Merged revisions 399553 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399554 65c4cc65-6c06-0410-ace0-fbb531ad65f3