HLS: do not discard packets when queuing explicit discontinuity

in case of explicit discontinuity (#EXT-X-DISCONTINUITY tag in the
playlist), do not discard packets that's already queued.

(when seeking, the old fetcher will be discarded so this won't affect
seeking case.)

Bug: 15020526
Change-Id: I5d3fc489df35e3bc44acb1ee7851571cb99cb56b
6 files changed