Don't try to remove peers without IPs from peers_by_ip

(closes issue ASTERISK-18696)
........

Merged revisions 341088 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@341089 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -27309,7 +27309,9 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 		found++;
 		/* we've unlinked the peer from the peers container but not unlinked from the peers_by_ip container yet
 		  this leads to a wrong refcounter and the peer object is never destroyed */
-		ao2_t_unlink(peers_by_ip, peer, "ao2_unlink peer from peers_by_ip table");
+		if (!ast_sockaddr_isnull(&peer->addr)) {
+			ao2_t_unlink(peers_by_ip, peer, "ao2_unlink peer from peers_by_ip table");
+		}
 		if (!(peer->the_mark))
 			firstpass = 0;
 	} else {