Properly remove empty leftover folders after rename

TorrentInfo::origFilePath will return the very original path from
.torrent file, not the most recent file path before the rename operation
and thus the code would not be working as we expected.

src/base/utils/string.h

@@ -31,8 +31,10 @@
 #define UTILS_STRING_H
 
 #include <QLatin1String>
+#include <QVector>
 
 class QString;
+class QStringRef;
 
 class TriStateBool;
 
@@ -66,6 +68,8 @@ namespace Utils
 
         bool parseBool(const QString &string, bool defaultValue);
         TriStateBool parseTriStateBool(const QString &string);
+
+        QString join(const QVector<QStringRef> &strings, const QString &separator);
     }
 }