Since keep_video started as None we always set it to keep_video_wish unless it was None, so in the end keep_video == keep_video_wish. This should have been changed in f3ff1a3696, but I didn't notice it.
On the tracks I tested the server number in the url from the webpage is valid
for the mp3 or the m4a file and any other number is invalid, it's a
waste of time to check them.
In Python 3, filter() returns an iterable object, which is equivalently
to True even for an empty result set. It causes false positive playlists
in generic extraction logic.