res_pjsip_refer: Fix occasional unexpected BYE sent after receiving a REFER.

res_pjsip_refer: Fix occasional unexpected BYE sent after receiving a REFER.

A race condition happened between initiating a transfer and requesting
that a dialog termination be delayed.  Occasionally, the transferrer
channels would exit the bridge and hangup before the dialog termination
delay was requested.

* Made request dialog termination delay before initiating the transfer
action.  If the transfer fails then cancel the delayed dialog termination
request.

ASTERISK-24755 #close
Reported by: John Bigelow

Review: https://reviewboard.asterisk.org/r/4460/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@432668 65c4cc65-6c06-0410-ace0-fbb531ad65f3