title: view considers navigation bar only after rotation
body: <p>I have a simple UIScrollView</p>
  
  <pre><code>UIScrollView *mainScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
  [self.view addSubview:mainScrollView];
  
  [mainScrollView mas_makeConstraints:^(MASConstraintMaker *make) {
      make.edges.equalTo(self.view);
  }];
  </code></pre>
  
  <p>When the view is loaded and shown, part of UIScrollView appears under the navigation bar. But after rotation the view is suddenly considers navigation bar and pins the view to its bottom.</p>
  
  <p><img src="https://i.stack.imgur.com/sG1LU.png" alt="http://i.stack.imgur.com/sG1LU.png">
  <img src="https://i.stack.imgur.com/bdwRW.png" alt="http://i.stack.imgur.com/bdwRW.png"></p>
  
  <p>How can I make a view consider navigation bar from the beginning?</p>