title: virtual-scroll returning empty Array
body: <p>HTML:</p>
  
  <pre><code>&lt;virtual-scroll [items]="items" (update)="viewPortItems = $event"&gt;    
                  &lt;div *ngFor="let item of viewPortItems"&gt;
                    {{item.name}}
                  &lt;/div&gt;                    
  &lt;/virtual-scroll&gt;
  </code></pre>
  
  <p>In component i am initializing the items.
  Component:</p>
  
  <pre><code>items = [{
          name: 'xyz'
      },
      {
          name: 'xyz'
      },
      {
          name: 'xyz'
      },
      {
          name: 'xyz'
      }
  ]
  </code></pre>
  
  <p>But in my page nothing is displayed. viewPortItems is empty.</p>