Fix download from URL (Web UI)

src/qtlibtorrent/qbtsession.h

@@ -123,7 +123,7 @@ public slots:
   void disableIPFilter();
   void setQueueingEnabled(bool enable);
   void handleDownloadFailure(QString url, QString reason);
-  void downloadUrlAndSkipDialog(QString url, QString save_path, QString label);
+  void downloadUrlAndSkipDialog(QString url, QString save_path=QString(), QString label=QString());
   // Session configuration - Setters
   void setListeningPort(int port);
   void setMaxConnections(int maxConnec);