Fix accidental calls to setAdapter(ListAdapter)

This issue took me a lot of time to understand. This code throws an `IllegalArgumentException`.

```java
BaseAdapter baseAdapter = new SomeBaseAdapter();
ListView listview = getListView(); // listView instance of DynamicListView
listView.setAdapter(baseAdapter); // IllegalArgumentException!!
```

But this don't:
```java
BaseAdapter baseAdapter = new SomeBaseAdapter();
DynamicListView listview = (DynamicListView) getListView();
listView.setAdapter(baseAdapter); // all ok
```

This PR prevents this strange behaviour.