title: How to scroll UITableView to a row *safely*?
body: <p>Sometimes when I tried to scroll a tableview to a row, I can unexpectedly supply a nonexistent section/row. And then the app will crash.</p>
  
  <pre><code>self.tableView.scrollToRow(at: IndexPath(row: targetRow, section: targetSection), at: UITableViewScrollPosition.bottom, animated: true);
  </code></pre>
  
  <p>How can I make this scrolling process crash-safe? I mean, if I do supply a nonexistent section/row, I want UITableView just ignore it. Or how can I check whether a section/row is exist or not within a UITableView before I do the scroll? Thanks.</p>