Missing check for number of bit-planes in j2kenc.c

[osamu620]

ffmpeg-ht/libavcodec/j2kenc.c

Line 813 in 043e106

prec->zerobits[pos].val = expn[bandno] + numgbits - 1 - cblk->nonzerobits;

This line might lead to overflow when (expn[bandno] + numgbits - 1) < cblk->nonzerobits becomes true because prec->zerobits[pos].val is uint8_t.

I propose to add a line for checking like

if ((expn[bandno] + numgbits - 1) < cblk->nonzerobits)
    av_log(avvtx, AV_LOG_ERROR, "Number of magnitude bit-planes is too big.\n");