Since 1d1d1fbff9 option-info/<name>/set-locally was being set to true
for every option. This broke setting start from ytdl-hook, which doesn't
overwrite start if it was set-locally. Fix this so that only adding an
option to reset-on-next-file or setting file-local-options/<name> make
set-locally true like before.
However, it's arguable that just adding an option to
reset-on-next-file without ever changing it should not make set-locally
true, so that e.g.
--reset-on-next-file=start 'https://youtube.com/watch?v=...&t=30'
will start at 30, though it currently doesn't.
Fixes#9081.
dd7a49eb71