avcodec/hevc_sei: Check payload size in decode_nal_sei_message()

Fixes: out of array access
Fixes: 29392/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-4821602850177024.fuzz

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

libavcodec/hevc_sei.c

@@ -463,6 +463,8 @@ static int decode_nal_sei_message(GetBitContext *gb, void *logctx, HEVCSEI *s,
         byte          = get_bits(gb, 8);
         payload_size += byte;
     }
+    if (get_bits_left(gb) < 8LL*payload_size)
+        return AVERROR_INVALIDDATA;
     if (nal_unit_type == HEVC_NAL_SEI_PREFIX) {
         return decode_nal_sei_prefix(gb, logctx, s, ps, payload_type, payload_size);
     } else { /* nal_unit_type == NAL_SEI_SUFFIX */