avcodec/hdrenc: Allocate more space

This needs to be double checked or a checking way of writing should be used

Fixes: out of array access
Fixes: 70007/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HDR_fuzzer-5478704150020096

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

libavcodec/hdrenc.c

@@ -124,7 +124,7 @@ static int hdr_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     uint8_t *buf;
     int ret;
 
-    packet_size = avctx->width * avctx->height * 4LL + 1024LL;
+    packet_size = avctx->height * 4LL + avctx->width * avctx->height * 8LL + 1024LL;
     if ((ret = ff_get_encode_buffer(avctx, pkt, packet_size, 0)) < 0)
         return ret;