avcodec/wavpack: Check value before shift in wp_exp2()

Fixes undefined shift, all callers should be changed to check the value
they use with wp_exp2() or its return value.

Fixes: 692/clusterfuzz-testcase-5757381516460032

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

libavcodec/wavpack.h

@@ -171,6 +171,8 @@ static av_always_inline int wp_exp2(int16_t val)
 
     res   = wp_exp2_table[val & 0xFF] | 0x100;
     val >>= 8;
+    if (val > 31)
+        return INT_MIN;
     res   = (val > 9) ? (res << (val - 9)) : (res >> (9 - val));
     return neg ? -res : res;
 }