riff: support ProRes in avi (APCN fourcc)
bgmc: fix sizeof arguments

CC: libav-devel@libav.org
Bug-Id: CID 608084 / CID 700724
exr: check return value

CC: libav-stable@libav.org
Bug-Id: CID 1198259
lpc: always initialize ref and err

CC: libav-stable@libav.org
Bug-Id: CID 29585 / CID 700759
atrac3plus: always initialize refwaves

CC: libav-stable@libav.org
Bug-Id: CID 1163851