Convert archive.org thumbnail url to absolute (Closes #18892)

[seasoprano]

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Thumbnail URL from archive.org is no longer absolute path as detailed in #18892 . This PR checks for the path and convert it into absolute.

[dstftw]

urljoin.

[dstftw]

This should be fixed in _parse_jwplayer_data.

[seasoprano]

This should be fixed in _parse_jwplayer_data.

Should I override that method then call super and modify the return value?

[dstftw]

No. Again: it must be fixed in InfoExtractor._parse_jwplayer_data.