Frédéric Yhuel authored Mar 26, 2012 and Hugo Beauzée-Luyssen committed Mar 29, 2012

This is needed for DASH module to work with (not yet ready) VLC MP4
demux. Forward seeking is implemented by calling Read() with a NULL
argument (= skipping), while backward seeking is limited to the current
block in the block_bytestream_t upon which is built the internal buffer.
This limitation is not really a problem because backward seeking will be
needed only for the parsing of the initialization fragment.

Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>