EntityTreeModel: fix to call private canFetchMore() everywhere
d33cab08 changed the public EntityTreeModel::canFetchMore() to always tell the view which is using the public API there is nothing more to fetch. But it missed to adapt the call in EntityTreeModel::hasChildren() which now also should call the internal variant.
Not aware of a related bug, seen while reading the code. Also no idea yet how to trigger that situation to test it. It just seems more correct now by my understanding :)