Check to make sure the channel pointer is present before queueing up an unhold frame on it. (issue #10046 reported by dimas)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@71412 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_agent.c

@@ -992,7 +992,7 @@ static struct ast_channel *agent_new(struct agent_pvt *p, int state)
 			ast_mutex_unlock(&p->lock);     /* For other thread to read the condition. */
 			return NULL;
 		}	
-	}
+	} else if (p->chan)
 		ast_indicate(p->chan, AST_CONTROL_UNHOLD);
 	p->owning_app = pthread_self();
 	/* After the above step, there should not be any blockers. */