Merged revisions 222543 via svnmerge from

https://origsvn.digium.com/svn/asterisk/trunk

................
  r222543 | dvossel | 2009-10-07 12:44:52 -0500 (Wed, 07 Oct 2009) | 14 lines
  
  Merged revisions 222542 via svnmerge from 
  https://origsvn.digium.com/svn/asterisk/branches/1.4
  
  ........
    r222542 | dvossel | 2009-10-07 12:41:21 -0500 (Wed, 07 Oct 2009) | 8 lines
    
    crash on transfer
    
    handle_invite_replaces() attempts to uplock a pvt's
    owner channel without first verifing that it exists.
    
    (issue #16027)
  ........
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git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.1@222545 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -17890,7 +17890,10 @@ static int handle_invite_replaces(struct sip_pvt *p, struct sip_request *req, in
 			can't harm */
 		transmit_response_with_sdp(p, "200 OK", req, XMIT_RELIABLE, FALSE);
 		/* Do something more clever here */
-		ast_channel_unlock(c);
+		if (c) {
+			*nounlock = 1;
+			ast_channel_unlock(c);
+		}
 		ast_channel_unlock(replacecall);
 		sip_pvt_unlock(p->refer->refer_call);
 		return 1;