Allow the odd empty segment to be skipped like a gap segment

[robwalch]

This PR will...

Treat the odd empty segment FRAG_PARSING_ERROR as a gap. The stream controller will advance to the next segment without loop loading. If subsequent errors occur, a level switch will be attempted, up to maxRetry count.

Why is this Pull Request needed?

Fixes regression of #4799 in v1.3 and v1.4 that introduced loop loading, and fatal errors after parsing errors accumulated beyond maxRetry count.

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

Some care was taken not to regress frag parsing error handling and gap jumping:

• No Error Event Attempting to Play Unsupported Video #5011 CC @mattzucker
• EXT-X-GAP  #2940 CC @mtoczko

For the sample streams provided in #5674 the empty segments are not needed and once the following segments are appended there are not gaps. The player does not recognize this to the case, and proceeds naively. In most cases we would want to switch variants when an error like this occurs to find an alternative, but in this case all variants are empty at the same playlist position. For that reason, this fix works well for that case, by avoiding switching. The problem is this may not work as well in cases where a better alternative would be found by switching down. In those cases, the down switch would not be made unless two consecutive errors occur.

Resolves issues:

Resolves #5674

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