Filip Roséen authored May 09, 2016 and Jean-Baptiste Kempf committed May 09, 2016

since we require two different ways of seeking depending on
DEMUX_SET_POSITION and DEMUX_SET_TIME has been recieved with precise
seeking or not, we now have two different seek functions within
matroska_segment_c.

The theory is quite simple:

    - matroska_segment_c::FastSeek is for future use

    - matroska_segment_c::Seek will find the lowest correct seekpoint
      for all our tracks combined, but set track.i_skip_until_fpos to
      the first block that needs to be decoded for a certain track.

      This means that decoding will start at the right location for
      every track, without us having to worry about decoding too much
      data for tracks that does not require such.

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