avfilter: add av_cold to init()

Signed-off-by: Paul B Mahol <onemda@gmail.com>
fate: add phase test

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avcodec/imc: Check flcoeffs5

Fixes infinite loop
Fixes Ticket2996

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