avcodec/ffv1dec: Fix integer overflow in read_quant_table()

Fixes: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'
Fixes: 3361/clusterfuzz-testcase-minimized-5065842955911168

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

libavcodec/ffv1dec.c

@@ -372,7 +372,7 @@ static int read_quant_table(RangeCoder *c, int16_t *quant_table, int scale)
     memset(state, 128, sizeof(state));
 
     for (v = 0; i < 128; v++) {
-        unsigned len = get_symbol(c, state, 0) + 1;
+        unsigned len = get_symbol(c, state, 0) + 1U;
 
         if (len > 128 - i || !len)
             return AVERROR_INVALIDDATA;