lavu/intreadwrite: add AV_[RW][BLN]48

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/transpose: support more pix fmts

Signed-off-by: Paul B Mahol <onemda@gmail.com>
swr: check channel layouts before using them.

Fixes out of array accesses

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