avcodec/ffv1dec: Fix off by 1 error with quant tables

Fixes: assertion failure
Fixes: 28447/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFV1_fuzzer-5369575948550144

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/ffv1dec.c

@@ -786,7 +786,7 @@ static int read_header(FFV1Context *f)
 
             if (f->version == 2) {
                 int idx = get_symbol(c, state, 0);
-                if (idx > (unsigned)f->quant_table_count) {
+                if (idx >= (unsigned)f->quant_table_count) {
                     av_log(f->avctx, AV_LOG_ERROR,
                            "quant_table_index out of range\n");
                     return AVERROR_INVALIDDATA;