Let's check if the torrent file can actually be opened before passing it to libtorrent

If we don't have enough permissions, libtorrent will spew a pretty useless, irrelevant and almost wrong message: "Failed to load the torrent: torrent file is not a dictionary"

src/gui/addnewtorrentdialog.cpp

@@ -177,6 +177,12 @@ bool AddNewTorrentDialog::loadTorrent(const QString& torrent_path)
         return false;
     }
 
+    QFileInfo fileinfo(m_filePath);
+    if (!fileinfo.isReadable()) {
+        MessageBoxRaised::critical(0, tr("I/O Error"), tr("The torrent file cannot be read from the disk. Probably you don't have enough permissions."));
+        return false;
+    }
+
     m_hasMetadata = true;
     QString error;
     m_torrentInfo = BitTorrent::TorrentInfo::loadFromFile(m_filePath, error);