fix signed shift overflow in WavpackOpenRawDecoder header parsing

[aizu-m]

UBSan from clang -fsanitize=shift, driving WavpackOpenRawDecoder with Matroska-style raw blocks (no "wvpk" header) whose reconstructed header bytes have the high bit set:

open_raw.c:163:41: runtime error: left shift of 128 by 24 places
  cannot be represented in type 'int'

The bytes promote to int before the << 24, so any top byte >= 0x80 overflows the sign bit. Cast to uint32_t for the six block_samples/flags/crc/block_size fields, as WavpackLittleEndianToNative already does.

[dbry]

Thanks!