file_scan_directory exceeds max execution time

There is a code in image.capthca.admin.inc on line 234 in function _image_captcha_settings_form_font_section which scans for fonts in the default files directory. When you have many files (I do have ~50K files - mainly images) in that directory the process takes "infinitely" long by exceeding the max exec time and resulting a blank page on the image captcha settings form.

    // We only show the name of fonts from the files directory
    // and do not provide a preview for security reasons:
    // files in files directory can be uploaded by normal or even anonymous
    // users and should not be trusted.
    //$fonts = _image_captcha_get_available_fonts_from_directories(array(file_directory_path()));