Improve resuming interrupted download when using yt-dlp or youtube-dl

Improve resuming interrupted download when using yt-dlp or youtube-dl

Fixes a failure like this:

curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume.

That happens because the whole web page has already been downloaded
previously, and kept, so now addurl tries to download it, and curl asks the
server to resume from the last byte. And youtube.com can't, for whatever
stupid reason.

So, delete the temp file after determining that youtube-dl can be used.