[downloader/hls] fix EXT-X-BYTERANGE off-by-one bug

[basicmaster]

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The end of the byte range is the first byte that is NOT part of the to
be downloaded range. So don't include it into the requested HTTP
download range, as this additional byte leads to a broken TS packet and
subsequently to e.g. visible video corruption.

Fixes #14748.

[basicmaster]

Note that the subtraction of 1 is only applied to the download itself (instead of directly to the byte_range array), as byte_range['end'] may be reused from a previous media segment, in a simpler form of an HLS playlist.

E.g. Reddit seems to use the byte range just to provide fast random access - all the media segments just cover the entire ES completely one-after-another. So you can verify the correct result by just downloading the video ES of a Reddit video before/after the fix and compare it with the plain file the applicable playlist refers to:

youtube-dl -f hls-871 https://www.reddit.com/r/BitchImATrain/comments/fg99jb/bitch_im_a_cow/

vs.

https://v.redd.it/tblt9361csl41/HLS_270.ts

[basicmaster]

I was wondering whether there is something new here, as this is a site-independent problem and possibly affects other sites than only Reddit...