avcodec/dvdec: dont try to decode ac when theres no input

fixes reading out of an empty bitstream

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec: fix old codec ids

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/gxf: fix old codec id

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