Error is never thrown when .ts fragments are continuously skipped

When `fragmentLoadSkipAfterMaxRetry = true` and `fragmentLoadMaxRetry` is set to a finite value flashls will be skipping .ts fragments till the end of the m3u8 playlist what could be undesirable. When the end of the playlist is reached then flashls skips and retries that last fragment in the endless loop.

Some threshold parameter e.g. `fragmentLoadSkipThreshold` should be introduced to define max count of skipped ts fragments before throwing an error.

Start by tracing the fragment loading and retry path controlled by fragmentLoadSkipAfterMaxRetry and fragmentLoadMaxRetry, then inspect how the final playlist fragment is handled. Define the skipped-fragment threshold behavior and verify that exceeding it terminates the endless retry loop by throwing an error.

Written by the indexing model from the issue text.