avcodec/wavpack: Fix runtime error: left shift of negative value -5

Fixes: 729/clusterfuzz-testcase-5154831595470848

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

libavcodec/wavpack.c

@@ -273,7 +273,7 @@ static inline int wv_get_value_integer(WavpackFrameContext *s, uint32_t *crc,
     unsigned bit;
 
     if (s->extra_bits) {
-        S <<= s->extra_bits;
+        S *= 1 << s->extra_bits;
 
         if (s->got_extra_bits &&
             get_bits_left(&s->gb_extra_bits) >= s->extra_bits) {