Prevent crash from trying to end a session in an invalid way.

This ensures that code that was only meant to be run on a reinvite failure
only runs on a reinvite failure.

(closes issue ASTERISK-22061)
reported by Rusty Newton



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@394473 65c4cc65-6c06-0410-ace0-fbb531ad65f3