dirac_parser: Improve parsing and silence pointless warnings

The parser scans for "BBCD" to appear in the bitstream which indicate a
parse info header and once that happens, checks if the parse offsets are
sane. Since random BBCD strings might appear in the bitstream the parser
will emit a pointless warning if that happens.

This commit improves parsing by checking for a valid parse code as well
as keeping the original checks for valid parse offsets. The warnings
were removed as they serve no real purpose.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
