apetag: do not require seekable output

Also don't write empty tags.

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avcodec/jpeg2000dec: Check Psot

Fixes out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/jpeg2000dec: check len before parsing header

Fixes out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>