Sometimes when opening a YouTube video with chapters, the chapter-list
ended up having all the chapters twice, despite the json from yt-dlp only
containing them once. That must mean that sometimes add_single_video()
runs twice before the chapter_list table gets cleared in the
on_preloaded hook.
This can be avoided by replacing chapter_list with a new table before
adding entries to it.
Christoph Heinrich
958fee6895