avformat/mxfdec; parse random index pack to get last partition offset and use it when footer partition offset is missing

Footer partition may not be present and even if present footer partition
offset may not be set in any partition except last one.

Signed-off-by: Paul B Mahol <onemda@gmail.com>
make it possible to compile ffmpeg without swscale

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avfilter/ff_insert_pad: fix order of operations

Fixes out of bounds access
Fixes CID732170
Fixes CID732169

No filter is known to use this function in a way so the issue can be reproduced.

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