Fix requireKeySystemAccessOnStart with live

[grabofus]

This PR will...

Fixes PIPELINE_ERROR_DECODE when transitioning from clear to encrypted content when the continuity preceeding the clear content either:

• is clear
• is encrypted but has no EXT-X-KEY (as it uses the key from the previous continuity)

Why is this Pull Request needed?

This PR allows falling back to using the key system from the config when non of the encrypted fragments are deemed usable from the manifest.

Are there any points in the code the reviewer needs to double check?

Is there a preference on

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[grabofus]

Issue reproducible with latest commit in master:

• load the test page
• wait for player to hit 1:30
• error happens:

Latest commit in master:
https://sample-videos-zyrkp2nj.s3-eu-west-1.amazonaws.com/test-20250422/test_20250704.9c0d46d.html

With this fix:
https://sample-videos-zyrkp2nj.s3-eu-west-1.amazonaws.com/test-20250422/test_20250704.a0a38dc.html

[robwalch]

Thanks for the contribution. I created #7384 as a followup to ensure that the setup in the first block works on first segment request. I also unblocked that path from requiring requireKeySystemAccessOnStart.

[robwalch]

@grabofus this change has been released in v1.6.7 along with two other changes to EME handling. Please let me know if your issue is resolved in latest.

[grabofus]

@robwalch I've checked latest (408bba3) and the issue is resolved, thank you!