Don't reset hangupcause if we already have one

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@66414 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -1934,7 +1934,7 @@ static int retrans_pkt(void *data)
 			usleep(1);
 			ast_mutex_lock(&pkt->owner->lock);
 		}
-		if (pkt->owner->owner) 
+		if (pkt->owner->owner && !pkt->owner->owner->hangupcause) 
 			pkt->owner->owner->hangupcause = AST_CAUSE_NO_USER_RESPONSE;
 		if (pkt->method == SIP_BYE) {
 			/* Ok, we're not getting answers on SIP BYE's. Who cares?