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.cpp

@@ -198,3 +198,14 @@ TriStateBool Utils::String::parseTriStateBool(const QString &string)
         return TriStateBool::False;
     return TriStateBool::Undefined;
 }
+
+QString Utils::String::join(const QVector<QStringRef> &strings, const QString &separator)
+{
+    if (strings.empty())
+        return {};
+
+    QString ret = strings[0].toString();
+    for (int i = 1; i < strings.count(); ++i)
+        ret += (separator + strings[i]);
+    return ret;
+}