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