Merged revisions 164350 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.4

........
  r164350 | file | 2008-12-15 14:11:21 -0400 (Mon, 15 Dec 2008) | 6 lines
  
  Do not try to unlock a non-existant channel if the transfer fails.
  (closes issue #13800)
  Reported by: dwagner
  Patches:
        asterisk-1.4.22-chan-sip-nullp.patch uploaded by tweety (license 608)
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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@164351 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -18371,7 +18371,9 @@ static int handle_request_invite(struct sip_pvt *p, struct sip_request *req, int
 			sip_pvt_unlock(p);
 			if (p->refer->refer_call) {
 				sip_pvt_unlock(p->refer->refer_call);
-				ast_channel_unlock(p->refer->refer_call->owner);
+				if (p->refer->refer_call->owner) {
+					ast_channel_unlock(p->refer->refer_call->owner);
+				}
 			}
 			p->invitestate = INV_COMPLETED;
 			return -1;