Merged revisions 319142 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.8

........
  r319142 | mnicholson | 2011-05-16 10:53:26 -0500 (Mon, 16 May 2011) | 8 lines
  
  Make sure tcptls_session exists before dereferencing it.
  
  (closes issue #19192)
  Reported by: stknob
  Patches:
        10-tcptls-unreachable-peer-segfault.patch uploaded by Chainsaw (license 723)
  Tested by: vois, Chainsaw
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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@319143 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -2758,7 +2758,7 @@ static void *_sip_tcp_helper_thread(struct sip_pvt *pvt, struct ast_tcptls_sessi
 	ast_debug(2, "Shutting down thread for %s server\n", tcptls_session->ssl ? "SSL" : "TCP");
 
 cleanup:
-	if (!tcptls_session->client && !authenticated) {
+	if (tcptls_session && !tcptls_session->client && !authenticated) {
 		ast_atomic_fetchadd_int(&unauth_sessions, -1);
 	}