Issue #2886549 by ufku: File name validation

    // Check type.

    if ($old_file->type == 'file') {

      // Delete dots and space at the beginning/end name.

      $new_name = trim($fm->getPost('new_name'), "\x00..\x1F.");

      // Crop string up to 50 characters.

      $new_name = mb_substr($new_name,0,50);

      $new_name = mb_substr($fm->getPost('new_name'),0,50);

      // Delete special symbols.

      $new_name = preg_replace('/[^\w_-]+/u', '', $new_name);

      $new_name = $new_name . '.' . pathinfo($old_name, PATHINFO_EXTENSION);