Avoiding setting an empty state (fallback to {})

I just faced a problem where I could optionally send data to the component via props:

```javascript
<MyComponent data={preloadedObject} />
```

Then I checked:

```javascript
getInitialStateAsync: function() {
    if (this.props.data) return false;
    return new Controller().get(this.props._id);
}
```

Returning nothing would break the rendering. This PR solves it.