avcodec/hq_hqa: Check available space before reading slice offsets

Fixes: Timeout (43sec -> 18sec)
Fixes: 14556/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HQ_HQA_fuzzer-5673543024508928

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

libavcodec/hq_hqa.c

@@ -248,6 +248,9 @@ static int hqa_decode_frame(HQContext *ctx, AVFrame *pic, size_t data_size)
     int width, height, quant;
     const uint8_t *src = ctx->gbc.buffer;
 
+    if (bytestream2_get_bytes_left(&ctx->gbc) < 8 + 4*(num_slices + 1))
+        return AVERROR_INVALIDDATA;
+
     width  = bytestream2_get_be16(&ctx->gbc);
     height = bytestream2_get_be16(&ctx->gbc);