title: Observable forkJoin not firing
body: <p>I'm trying to use <code>forkJoin</code> on two Observables. One of them starts as a stream... If I subscribe to them directly I get a response, <code>forkJoin</code> isn't firing though. Any ideas?</p>
  <pre><code>private data$: Observable&lt;any[]&gt;;
  private statuses$: Observable&lt;any[]&gt;;
  private queryStream = new Subject&lt;string&gt;();    
  
  ....
  
  this.data$ = this.queryStream
      .startWith('')
       .flatMap(queryInput =&gt; {
              this.query = queryInput
              return this._companyService.getCompanies(this.queryRequired + ' ' + this.query, this.page, this.sort);
                  })
              .share();
      
  ...
  
  Observable.forkJoin(this.statuses$, this.companies$)
              .subscribe(res =&gt; {
                  console.log('forkjoin');
                  this._countStatus(res[0], res[1]);
              });
  
  
  // This shows arrays in the console...
  
  this.statuses$.subscribe(res =&gt; console.log(res));
  this.companies$.subscribe(res =&gt; console.log(res));
  
  // In the console
  Array[9]
  Array[6]
  </code></pre>