one-way-number-mask types one or many "0" characters in odd circumstances

I've written these two failing tests for `one-way-number-mask-test.js`.

```js
test('It does not input a zero when hitting "."', async function(assert) {
await render(hbs``);
await fillIn('input', '.');

assert.dom('input').hasValue('');
});

test('It does not input a zero when hitting "m"', async function(assert) { // This also happens with the letter `k`
await render(hbs``);
await fillIn('input', 'm');

assert.dom('input').hasValue('');
});
```