refactor: `getOptions` should return an `{}` by default 

Currently if no loader options are set, `getOptions(this)` returns `null` by default, which requires a fallback to avoid breaking further `options.x` references within the loader.

```js
const options = loaderUtils.getOptions(this)
````

Is that intended for some reason or would it be possible to return an empty `{}`by default instead ?