Minor bugfix: Ensure the admin panel does not show expired but not yet deleted files.
Background: Expired files are not immediately cleaned up from the database and disk. Instead, an automatic task cleans up expired files every 15 minutes. The download page and endpoint take this into account, i.e. they check the expiry timestamp and refuse to serve files that are still on disk but have already expired. The admin panel showing all the files did not perform this check - now it does!