Agent's should not try to call a channel's indicate callback

if the channel has been hung up. It will likely crash
otherwise

ABE-1159



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@141366 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_agent.c

@@ -666,7 +666,7 @@ static int agent_indicate(struct ast_channel *ast, int condition, const void *da
 	struct agent_pvt *p = ast->tech_pvt;
 	int res = -1;
 	ast_mutex_lock(&p->lock);
-	if (p->chan)
+	if (p->chan && !ast_check_hangup(p->chan))
 		res = p->chan->tech->indicate ? p->chan->tech->indicate(p->chan, condition, data, datalen) : -1;
 	else
 		res = 0;