title: TableView yOffset changed after reloadData
body: <p>when i custom the <code>tableHeaderView</code>, after i <code>reloadData</code> in <code>viewWillAppear</code>, the tableView <code>contentOffset.y</code> will be changed. </p>
  
  <p>Please help me..</p>
  
  <hr>
  
  <p>I have log the tableView contentOffset when i will invoke <code>reloadData</code>,
  this is the log:</p>
  
  <p><code>2016-03-01 10:51:04:362 ~~[1474:387143] will-TableViewContentOffset: {0, -18}
  2016-03-01 10:51:04:363 ~~[1474:387143] did-TableViewContentOffset: {0, -62}</code></p>
  
  <p>this is how i invoked:</p>
  
  <pre><code>    NHDLog(@"will-TableViewContentOffset: %@", NSStringFromCGPoint(self.tableView.
  
      [self _reloadTableView];
  
      NHDLog(@"did-TableViewContentOffset: %@", NSStringFromCGPoint(self.tableView.contentOffset));
  </code></pre>
  
  <p>In <code>viewDidLoad</code> i have set:</p>
  
  <pre><code>self.edgesForExtendedLayout = UIRectEdgeNone;
  self.automaticallyAdjustsScrollViewInsets = NO;
  </code></pre>