fix OOB write in JPEG DHT parsing when sizes sum > 256#352
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A crafted DHT marker can hand
JpegHuffman::Buildacount[]whose 16 entries sum well past 256 (max 16*255 = 4080). The first inner loop then writessize[k++]past the 257-bytesizemember ofJpegHuffman, and the follow-upfor (i=0; i<n; ++i) v[i] = stream->Get8u();in the0xC4handler overrunsvalues[256]with attacker-controlled bytes. Rejecttotal > 256up front in both the Base and AVX2 stb-derived decoders.