An accumulation of several fixes:
1. Change to HlsExtractorWrapper is just a move + documentating
things that were already true + adding a precondition in the
configureSpliceTo method.
2. Change in HlsSampleSource.readData ensures that configureSpliceTo
and hasSamples aren't called on an extractor that isn't prepared.
3. The other change in HlsSampleSource ensures the correct "previous"
TsChunk is used. If a TsChunk fails to load and is replaced, the
previous chunk should be the one before that whose load completed
successfully.
4. Determine switchingVariantSpliced based on the actual format of the
previous chunk, so it's set correctly in the case of a TsChunk load
failure and subsequent replacement.
b8df8ecb47