- Use timestampOffsetUs == C.TIME_UNSET directly as the way of
determining whether the adjuster has determined the offset,
rather than relying on lastSampleTimestampUs checks for this.
- Remove comment referring to lastSampleTimestampUs as holding
the "adjusted PTS". Its value may not have originated from a PTS
timestamp. It's also confusing to refer to it as "adjusted"
given timestampOffsetUs has not been applied to it.
- Fix PassthroughSectionPayloadReader to make sure it'll never
output a sample with an unset timestamp.
#minor-release
PiperOrigin-RevId: 388226180
