Fix error message when websockets http_dir directory does not exist.

ChangeLog.txt

@@ -5,6 +5,7 @@ Broker:
 - Don't error on zero length persistence files. Closes #316.
 - For http only websockets clients, close files served over http in all cases
   when the client disconnects. Closes #354.
+- Fix error message when websockets http_dir directory does not exist.
 
 Client library:
 - Clients can now use TLS with IPv6.

src/websockets.c

@@ -656,7 +656,7 @@ struct libwebsocket_context *mosq_websockets_init(struct _mqtt3_listener *listen
 		if(!user->http_dir){
 			_mosquitto_free(user);
 			_mosquitto_free(p);
-			_mosquitto_log_printf(NULL, MOSQ_LOG_ERR, "Error: Unable to open http dir \"%s\".", user->http_dir);
+			_mosquitto_log_printf(NULL, MOSQ_LOG_ERR, "Error: Unable to open http dir \"%s\".", listener->http_dir);
 			return NULL;
 		}
 	}