vp8: use a fixed-size edge emu buffer

The reason is the same as for e588615d938f8581f0d6f3771662d08cadfc00de

Based on a patch by Ronald S. Bultje <rsbultje@gmail.com>
h264: reset data partitioning at the beginning of each decode call

Prevents using GetBitContexts with data from previous calls.

Fixes access to freed memory.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
Merge commit 'e46ad30a808744ddf3855567e162292a4eaabac7'

* commit 'e46ad30a808744ddf3855567e162292a4eaabac7':
  vp8: use a fixed-size edge emu buffer

Conflicts:
	libavcodec/vp8.c
	libavcodec/vp8.h

See: face578d56c2d1375e40d5e2a28acc122132bc55
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '1f097d168d9cad473dd44010a337c1413a9cd198'

* commit '1f097d168d9cad473dd44010a337c1413a9cd198':
  h264: reset data partitioning at the beginning of each decode call

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/vc1dec: vc1_pred_b_mv() is not used for fields, simplify code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/vc1dec: remove blocks_off use from vc1_pred_b_mv()

it should always be 0

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>