Ensure that SDP read from TCP socket is null-terminated.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@218504 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -2967,6 +2967,7 @@ static void *_sip_tcp_helper_thread(struct sip_pvt *pvt, struct ast_tcptls_sessi
 					ast_mutex_unlock(&tcptls_session->lock);
 					goto cleanup;
 				}
+				buf[sizeof(buf)-1] = '\0';
 				ast_mutex_unlock(&tcptls_session->lock);
 				if (me->stop)
 					goto cleanup;