The FileList that is read with GetTorrents is empty, as it's only loaded with
GetTorrentById. So, always insert the new FileList on the database, and rely on
the unique_index to avoid duplications.
It used to update only torrents with NULL or 0 filesizes, setting
both their filesizes and the file lists. Now, it looks for both
NULL or 0 filesizes and empty file lists.
