avcodec/exr: Fix preview overflow

Fixes: CID1515456 Unintentional integer overflow

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/exr.c

@@ -1943,7 +1943,7 @@ static int decode_header(EXRContext *s, AVFrame *frame)
                                                      "preview", 16)) >= 0) {
             uint32_t pw = bytestream2_get_le32(gb);
             uint32_t ph = bytestream2_get_le32(gb);
-            uint64_t psize = pw * ph;
+            uint64_t psize = pw * (uint64_t)ph;
             if (psize > INT64_MAX / 4) {
                 ret = AVERROR_INVALIDDATA;
                 goto fail;