mpeg4video: Initialize xvididct for all threads

Signed-off-by: Diego Biurrun <diego@biurrun.de>
huffyuv: K&R formatting cosmetics
huffyuv: Eliminate some pointless casts
huffyuv: Use avpriv_report_missing_feature() where appropriate
huffyuv: Return proper error codes
huffyuv: Check and propagate function return values

Bug-Id: CVE-2013-0868

inspired by a patch from Michael Niedermayer <michaelni@gmx.at>
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Diego Biurrun <diego@biurrun.de>

CC: libav-stable@libav.org