avcodec/dvdsubdec: Check all fseek()s return codes

Fixes CID1254660

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/vorbis_parser: Move vp check

Fixes null pointer dereference
Fixes CID1251347

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avdevice/xcbgrab: Fix/remove unneeded NULL checks

Fixes CID1254664

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mpeg: fix memleak of sub_name on error

Fixes CID1254666

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