Suppress multiple I/O errors for the same torrent

When a file error happens libtorrent spews a ton of `file_error_alert`
which result in log floods and notification balloon floods. The later
might render the program inaccessible because the constant
notifications prevent the user from interacting with the tray icon.

Closes #8934

src/base/bittorrent/session.h

@@ -761,6 +761,10 @@ namespace BitTorrent
         QStringMap m_categories;
         QSet<QString> m_tags;
 
+        // I/O errored torrents
+        QSet<InfoHash> m_recentErroredTorrents;
+        QTimer *m_recentErroredTorrentsTimer;
+
 #if LIBTORRENT_VERSION_NUM < 10100
         QMutex m_alertsMutex;
         QWaitCondition m_alertsWaitCondition;