v1.6.39 - Closes a gap in the check for playlists disguised as video

Since 1.6.20 the server refuses a torrent whose "video" file is really a playlist, by reading the
file's first bytes before the probe opens it. A torrent built to deliver only part of those bytes
in time could get past that check. The server now refuses any file whose first bytes it could not
read in full.

Upgrade: pull it.