title: Observable.Create doesn't work and Observable.ToEnumerable blocks indefinitely
body: <p>Why the code below doesn't work?</p>
  
  <pre><code>var observable = Observable.Create&lt;int&gt;(o =&gt; new Action(() =&gt;
  {
      o.OnNext(0);
      o.OnCompleted();
  }));
  
  foreach (var item in observable.ToEnumerable()) // &lt;-- Here blocks
  {
      // Never get here
  }
  </code></pre>
  
  <p>The below doesn't work neither:</p>
  
  <pre><code>Task.Run(() =&gt;
  {
      foreach (var item in observable.ToEnumerable()) // &lt;-- Still blocks
      {
          // Never get here
      }
  }).Wait();
  </code></pre>
  
  <p>Interestingly, the Generate method works as expected:</p>
  
  <pre><code>var observable = Observable.Generate(0, i =&gt; i &lt; 1, i =&gt; i + 1, i =&gt; i);
  
  foreach (var item in observable.ToEnumerable())
  {
      // Is ok
  }
  </code></pre>