"Cannot read property 'didChange' of undefined" when upgrading from 1.13.1 to 1.13.2

After updating from 1.13.1 to 1.13.2 (that changed setProperties to internalModel#setupData) we've started getting `Cannot read property 'didChange' of undefined` when saving a record that has nested fragments.

**Trace**:

```
TypeError: Cannot read property 'didChange' of undefined
at chainsDidChange (ember.debug.js:20537)
at propertyDidChange (ember.debug.js:20417)
at iterDeps (ember.debug.js:20504)
at dependentKeysDidChange (ember.debug.js:20460)
at Object.propertyDidChange (ember.debug.js:20414)
at exports.default._emberMetalMixin.Mixin.create.propertyDidChange (ember.debug.js:36766)
at exports.default._emberMetalMixin.Mixin.create.notifyPropertyChange (ember.debug.js:36780)
at Ember.Object.extend._notifyProperties (model.js:564)
at InternalModel.ember$data$lib$system$model$internal$model$$InternalModel.setupData (internal-model.js:196)
at model$fragments$lib$fragments$fragment$$setFragmentData (fragment.js:191)
```

**Setup**:

``` js
// Setup is something like this:

// model.js
export default DS.Model.extend({
sections: MF.fragmentArray('section')
)};

// section.js
export default MF.Fragment.extend({
subSections: MF.fragmentArray('sub-section')
});

// sub-section.js
export default MF.Fragment.extend({
...
});
```

**Steps to reproduce**:
- load a model with nested fragments into the store
- save the model
- TypeError

**note**: this only seems to happen if:
- the nested fragment (`sub-section`) is present
- **the nested fragment was not changed** (if it's dirty the error is not triggered)

ember: 1.13.10
ember data: 1.13.15

I'll try to find a way to reproduce this outside of our app or write a failing test when I have some more time.

Start at fragment.js:191 and internal-model.js:196, then inspect model.js:564 along the traced save path. Reproduce with nested fragments where the sub-section is unchanged, and add the failing test the report calls for. Done means saving that setup no longer raises the TypeError and the regression is covered.

索引モデルが issue の本文から書いたものです。