HLS broken again by M3U

because of HLS checks removal by 0b67edc9

and no longer whitelisting of extensions by cc7762fd

HLS now forcefully goes into m3u demuxer in case of m3u extension.

1 - 0b67edc9 needs a revert or the core needs to handle preparse skipping (we do not preparse adaptive content).

2 - cc7762fd should restore whitelisting, and/pr the translation into forced demux should re-prioritize probing, never enforce.

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