avcodec/pnmdec: Use 64bit for input size check

Fixes: out of array read
Fixes: poc3

Reported-by: VulDB CNA Team
Found-by: CookedMelon
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 3faadbe2a2)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/pnmdec.c

@@ -264,7 +264,7 @@ static int pnm_decode_frame(AVCodecContext *avctx, AVFrame *p,
         break;
     case AV_PIX_FMT_GBRPF32:
         if (!s->half) {
-            if (avctx->width * avctx->height * 12 > s->bytestream_end - s->bytestream)
+            if (avctx->width * avctx->height * 12LL > s->bytestream_end - s->bytestream)
                 return AVERROR_INVALIDDATA;
             scale = 1.f / s->scale;
             if (s->endian) {