write test and potential fix for https://github.com/jsillitoe/react-currency-input/issues/91

[ericblade]

jsillitoe#91

You can reproduce using

<CurrencyInput
            prefix="$ "
            precision={0}
            suffix=",00"
            decimalSeparator=","
            thousandSeparator="."
            allowEmpty
            placeholder="buggy"
            value={null}
            onChangeEvent={(v1,v2,v3) => console.log(v1,v2,v3)}
          />