avcodec/ylc: Fix vlc of 31 bits

Fixes: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'
Fixes: 2515/clusterfuzz-testcase-minimized-6197200012967936

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

libavcodec/ylc.c

@@ -69,7 +69,7 @@ static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
 
     s = nodes[node].sym;
     if (s != -1) {
-        bits[*pos] = (~pfx) & ((1 << FFMAX(pl, 1)) - 1);
+        bits[*pos] = (~pfx) & ((1U << FFMAX(pl, 1)) - 1);
         lens[*pos] = FFMAX(pl, 1);
         xlat[*pos] = s + (pl == 0);
         (*pos)++;