Fix #1567 and add tests to cover getChildView taking a model

```diff
+ expect(this.collectionView.getChildView).to.have.been.calledTwice.and.calledWith(this.collection.models[0], this.collection.models[1])
- expect(this.collectionView.getChildView).to.have.been.calledTwice;
- expect(this.collectionView.getChildView).to.have.been.calledWith(this.collection.models[0]);
- expect(this.collectionView.getChildView).to.have.been.calledWith(this.collection.models[1]);
```