If a timeline update removed periods at the end of the timeline which
had been buffered, handleSourceInfoRefreshed would call
getNextPeriodIndex and get back -1 for the last period holder in the
new timeline. Then isLastPeriod(-1) could throw.
Fix this behavior so that the remainder of the timeline is discarded.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=156061016
