Convert a wordArray to Uint8Array

@param {Uint8Array} destUa - A destination Uint8Array
@param {WordArray} cryptowords - A wordArray

@return {Uint8Array}
function(destUa, cryptowords) {
    for (let i = 0; i < destUa.length; i += 4) {
        let v = cryptowords.words[i / 4];
        if (v < 0) v += 0x100000000;
        destUa[i] = (v >>> 24);
        destUa[i + 1] = (v >>> 16) & 0xff;
        destUa[i + 2] = (v >>> 8) & 0xff;
        destUa[i + 3] = v & 0xff;
    }
    return destUa;
}