Account for possible NULL pointer when we receive a 408 in response to a REGISTER

It may be that by the time we receive a reply to a REGISTER request, the attempt has
timed out and thus the registry structure pointed to by the corresponding sip_pvt has
gone away. This situation was handled properly for a 200 OK response, but the 408
case assumed that the sip_registry struct was non-NULL, thus potentially causing a crash

This commit fixes this assumption and prints out a message to the console if we should
receive a late 408 response to a REGISTER


(closes issue #14211)
Reported by: aborghi
Patches:
      14211.diff uploaded by putnopvut (license 60)
Tested by: aborghi



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@168975 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -12698,7 +12698,11 @@ static int handle_response_register(struct sip_pvt *p, int resp, char *rest, str
 		break;
 	case 408:	/* Request timeout */
 		/* Got a timeout response, so reset the counter of failed responses */
-		r->regattempts = 0;
+		if (r) {
+			r->regattempts = 0;
+		} else {
+			ast_log(LOG_WARNING, "Got a 408 response to our REGISTER on call %s after we had destroyed the registry object\n", p->callid);
+		}
 		break;
 	case 479:	/* SER: Not able to process the URI - address is wrong in register*/
 		ast_log(LOG_WARNING, "Got error 479 on register to %s@%s, giving up (check config)\n", p->registry->username,p->registry->hostname);