The palette is organised into 'hold' and 'modify' pairs, hence why
the first palette entry is pal[1].

Fixes ticket #1701.
Signed-off-by: Peter Ross <pross@xvid.org>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>