title: Mat-tab material angular6 selectedIndex doesn't work with *ngFor
body: <p>I display several tabs with a loop ngFor using Angular Material tabs.
  This works properly however now I would like to open the second tab when initialised and not the first tab.
  Therefore, I add the property selectedIndex in the mat-tab-group but it doesn't work and still continues to open on the first tab.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;mat-tab-group class="col-10 offset-1" (selectedTabChange)="onTabChanged($event)" [selectedIndex]="1"&gt;
    &lt;mat-tab label={{tab.name}} *ngFor="let tab of tabs; let index = index"&gt;
      &lt;div&gt;
        Values: {{tab.values}}
      &lt;/div&gt;
    &lt;/mat-tab&gt;
  &lt;/mat-tab-group&gt;
  </code></pre>
  
  <p>The variable <em>"tabs"</em> is fetched with a service from the server in ngOnInit like this:</p>
  
  <p><strong>COMPONENT</strong></p>
  
  <pre><code>this.api.getDataset(this.route.snapshot.params["experimentid"]).subscribe(
    res =&gt; {
      this.tabs = res;
    },
    err =&gt; {
      console.log(err);
    }
  );
  </code></pre>
  
  <p>I think it comes from here because if I set the tabs manually without requesting to the server it works. Like this:</p>
  
  <pre><code>this.tabs = [{name: "X2", values: "52"}, {name: "Z2", values: "52"}, {name: "R2", values: "52"}]
  </code></pre>