avcodec/ffv1dec: Check quant table symbols more completely

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/ffv1dec.c

@@ -476,7 +476,7 @@ static int read_quant_table(RangeCoder *c, int16_t *quant_table, int scale)
     for (v = 0; i < 128; v++) {
         unsigned len = get_symbol(c, state, 0) + 1;
 
-        if (len > 128 - i)
+        if (len > 128 - i || !len)
             return AVERROR_INVALIDDATA;
 
         while (len--) {