@child() decorator does not work properly in combination with if.bind

**I'm submitting a bug report**

* **Library Version:**
1.10.2

**Please tell us about your environment:**
* **Operating System:**
Windows 10

* **Node Version:**
10.16.3

* **NPM Version:**
6.12.0

* **JSPM OR Webpack AND Version**
JSPM 0.16.53

* **Browser:**
all

* **Language:**
all

**Current behavior:**
Let's say we have an app, which uses the component `simple-component`. This component is placed inside container which is added/removed conditionally. This component uses `@child()` decorator to reference an `input` element.

**app.html**
```html

Toggle Containers

```

**app.ts**
```typescript
export class App {
showMainContainer: boolean = true;

toggleContainers() {
this.showMainContainer = !this.showMainContainer;
}
}
```

**simple-component.html**
```html

Some Input Suffix

```

**simple-component.ts**
```typescript
import {child} from 'aurelia-templating';

export class SimpleComponent {
@child('input') myInput: any;

attached() {
console.log('myInput: ', this.myInput);
}
}
```

On initial load, reference in `myInput` property is correct. But if we click "Toggle Containers" button two times (to remove and add `cointainer-1` element to the DOM again) then `myInput` property points to `null`. I noticed that current behaviour is caused by this commit: https://github.com/aurelia/templating/commit/7989015. In previous versions of this plugin everything worked fine, even in scenario described above.

**Expected/desired behavior:**

* **What is the expected behavior?**

Component's property decorated with `@child` decorator should reference appropriate element even if component's parents are added or removed conditionally.

Start by reproducing the reported behavior using the app.html, app.ts, simple-component.html, and simple-component.ts examples in the issue. Then read the linked commit, 7989015, and investigate how @child('input') behaves when the component's parent is removed and added by if.bind; done means myInput still references the input after toggling twice.

Written by the indexing model from the issue text.