ts: fix demuxing of BluRay streams.

ts: fix demuxing of BluRay streams.

BluRay streams have 4-byte header before TS sync byte. Current code handles 192-byte ts packets,
but it assumes extra bytes are at the end of packet. This results in re-sync at stream start:
  1) first packet is dropped
     First packet is usually PAT, and losing it means losing the first GOP.
     This is fatal with still-image based menus.
  2) 4-byte header of the second packet is skipped
     This results in read of the last packet returning only 188 bytes,
     and it is also skipped.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>