growTextarea may be called against destroyed component

Using `1.0.0-beta.2`, I had the following error reported to sentry:

> Cannot read property 'addClass' of undefined

From the `growTextarea` method.

The code looks like this:

```javascript
let inputElement = this.$('input, textarea');
inputElement.addClass('md-no-flex').attr('rows', 1);
```

We probably just miss a check against 'isDestroying' and 'isDestroyed' before trying to apply `growTextarea`.