title: Session.getActiveSession() returns null when starting the app, although I'm connected
body: <p>I use com.facebook.widget.UserSettingsFragment to manage login/logout to Facebook in my app:</p>
  
  <pre><code>UserSettingsFragment userSettingsFragment = new UserSettingsFragment();
  Session session = Session.getActiveSession();
  if(session==null || session.isClosed()){
      userSettingsFragment.setPublishPermissions(Arrays.asList("publish_actions"));
  }
  fragmentTransaction.replace(R.id.content_container, userSettingsFragment, "userSettingsFragment");
  </code></pre>
  
  <p>In another <code>Fragment</code> (but same <code>Activity</code>), Before publishing on Facebook I'm checking whether I'm logged using</p>
  
  <pre><code>Session session = Session.getActiveSession();
  if (session != null &amp;&amp; session.isOpened()){
      publishOnFacebook(intent.getExtras());
  }
  </code></pre>
  
  <p>When I start my app and try to publish, I always get a <code>null</code> <code>Session</code> although I logged in before. And when I start <code>UserSettingsFragment</code>, it shows me that I'm connected.</p>
  
  <p>How can <code>Session.getActiveSession();</code> be <code>null</code> if I'm actually connected?</p>
  
  <p>Moreover, if I I start the <code>Fragment</code> where I do the publishing straight after <code>UserSettingsFragment</code>, I get the correct <code>Session</code>, i.e.:</p>
  
  <pre><code>1 start the app
  2 call `Session.getActiveSession()` in another `Fragment` returns `null`
  3 start `UserSettingsFragment` shows that I'm log
  </code></pre>
  
  <p>but</p>
  
  <pre><code>1 start the app
  2 start `UserSettingsFragment` shows that I'm log
  3 call `Session.getActiveSession()` in another `Fragment` returns a session
  </code></pre>
  
  <p>Anybody can help?</p>