Lock iax2 pvt structure when passing off to the AMI function, and make sure it exists. (issue #9674 reported by arabe)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@63182 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_iax2.c

@@ -3343,7 +3343,10 @@ static int iax2_answer(struct ast_channel *c)
 	unsigned short callno = PTR_TO_CALLNO(c->tech_pvt);
 	if (option_debug)
 		ast_log(LOG_DEBUG, "Answering IAX2 call\n");
-	iax2_ami_channelupdate(c->tech_pvt);
+	ast_mutex_lock(&iaxsl[callno]);
+	if (iaxs[callno])
+		iax2_ami_channelupdate(iaxs[callno]);
+	ast_mutex_unlock(&iaxsl[callno]);
 	return send_command_locked(callno, AST_FRAME_CONTROL, AST_CONTROL_ANSWER, 0, NULL, 0, -1);
 }