Sticky Query Params Failing in Engine with Loading Template

This PR ended up presenting some issues in my application after updated to `v2.12.0` and Ember-Engines `v0.5.0`: https://github.com/emberjs/ember.js/pull/14794

It does look like this might be an existing and known issue (see https://github.com/emberjs/ember.js/issues/12107) – however, because I am only experiencing this with an Engine and only after upgrading, I figured it was worth opening a new issue.

I've created a failing test that reproduces the issue here: https://github.com/emberjs/ember.js/pull/15050

A quick explanation (this is the same example in the failing test case):

Let's say we have this `routes.js` file in our engine:

```js
this.route('contributor', { path: 'contributor/:id' }, function() {
this.route('posts');
this.route('profile');
});
```

And, our `contributor` controller has a `queryParameter` of `simplified`, which is currently set to the non-default value of `true`.

Also, `contributor/posts` has a slow-loading model and we have a loading template at `contributor/loading.hbs`.

`contributor/posts.hbs` also has a template which contains a link to profile: `{{#link-to "blog.contributor.posts"}}Posts{{/link-to}}`

If we navigate to `contributor/1/posts?simplified=true`, then the link to `blog.contributor.posts` will not contain the `simplified=true` queryParameter as expected.

----

The best I could figure out was that during the `intermediateTransitionTo` (which is the initial transition), the query parameter cache key includes `undefined` when it should contain the `id` of the model for `contributor` (1 in this case).

In fact, the test will pass if we navigate to `contributor/undefined/posts?simplified=true` as it tricks the qpCache key.