title: Navigation bar disappears when typing in UISearchController text field
body: <p>I'm trying to figure out why my whole navigation bar disappears when I start typing in the UISearchController.searchBar  It loads properly and animates properly, but I lose the active NavBar when I start typing.  Here's the code to load the searchController from viewDidLoad:</p>
  
  <pre><code>    UITableViewController *searchResultsController = [[UITableViewController alloc] initWithStyle:UITableViewStylePlain];
  
      searchResultsController.tableView.dataSource = self;
      searchResultsController.tableView.delegate = self;
      searchResultsController.tableView.backgroundColor = [UIColor redColor];    
  
      self.searchController = [[UISearchController alloc] initWithSearchResultsController:searchResultsController];
      self.searchController.delegate = self;
      self.searchController.searchResultsUpdater = self;
      self.searchController.dimsBackgroundDuringPresentation = YES;
      self.searchController.hidesNavigationBarDuringPresentation = NO;
  
      [self.searchController.searchBar sizeToFit];
  
      self.tableView.tableHeaderView = self.searchController.searchBar;
      self.definesPresentationContext = NO;
  </code></pre>
  
  <p>And here's the result after I start typing:</p>
  
  <p><img src="https://i.stack.imgur.com/qRygQ.png" alt="enter image description here"></p>
  
  <p>Notice how the table view is there, but it appears to occupy the space of the nav controller and extend downwards into the first section heading.  Any ideas?</p>
  
  <p>Thanks.</p>