gifdec: convert to bytestream2

(cherry picked from commit 1f3e56b6dcc163a705704e98569d4850a31d651c)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>
lzw: switch to bytestream2

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
(cherry picked from commit e89aa4bf56e5b5c45f569eb12733519789e057da)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>
pmpdec: check that there is at least one audio packet.

The code cannot handle there being none, but that should not happen for
valid files.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org
(cherry picked from commit 1b5d065ca722eb8028c7a08e054b6da3419faf5d)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>
lavr: check that current_buffer is not NULL before using it

Fixes a segfault during resampling when compiled with -DDEBUG.
Fixes all fate-lavr-resample tests with -DDEBUG.

CC:libav-stable@libav.org
(cherry picked from commit 211ca69b13eb0a127a9ef7e70ddaccdab125d1c5)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>
mpegvideo: Drop a faulty assert

That check is easily reachable by faulty input.

CC:libav-stable@libav.org
Reported-by: Torsten Sadowski <tsadowski@gmx.net>
(cherry picked from commit 72072bf9de3241848ea86f68d2297b7a5d6ad49b)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>
Merge commit '0e8ae6d10c609bb968c141aa2436413a55852590' into release/1.1

* commit '0e8ae6d10c609bb968c141aa2436413a55852590':
  mpegvideo: Drop a faulty assert
  lavr: check that current_buffer is not NULL before using it
  pmpdec: check that there is at least one audio packet.
  lzw: switch to bytestream2
  gifdec: convert to bytestream2

Conflicts:
	libavcodec/gifdec.c
	libavcodec/lzw.c
	libavcodec/lzw.h
	libavformat/pmpdec.c

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