Widget/ItemList: fix getData() to not make up entries if empty

If getData() is called on a empty ItemList widget,
it currently makes up 3 bogus items and returns, like this:

```
array(3) {
  [0] =>
  array(1) {
    'title' =>
    array(0) {
    }
  }
  [1] =>
  array(1) {
    'label' =>
    array(0) {
    }
  }
  [2] =>
  array(1) {
    'description' =>
    string(0) ""
  }
}
```

This patch fixes that
You don't need to add this line if phpunit is installed via composer. Please, removed it. The rest is ok, I'll merge as soon as you fix this.