fix monitor thread issue, even though commented out

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@1983 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_mgcp.c

@@ -3043,7 +3043,7 @@ int unload_module()
 		return -1;
 	}
 	if (!ast_mutex_lock(&monlock)) {
-		if (monitor_thread) {
+		if (monitor_thread && (monitor_thread != -2)) {
 			pthread_cancel(monitor_thread);
 			pthread_kill(monitor_thread, SIGURG);
 			pthread_join(monitor_thread, NULL);