avcodec/exr: Check ymin vs. h

Fixes: out of array access
Fixes: 26532/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-5613925708857344
Fixes: 27443/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-5631239813595136

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/exr.c

@@ -1830,7 +1830,7 @@ static int decode_frame(AVCodecContext *avctx, void *data,
     // Zero out the start if ymin is not 0
     for (i = 0; i < planes; i++) {
         ptr = picture->data[i];
-        for (y = 0; y < s->ymin; y++) {
+        for (y = 0; y < FFMIN(s->ymin, s->h); y++) {
             memset(ptr, 0, out_line_size);
             ptr += picture->linesize[i];
         }