title: get IndexPath for a collectionview header without row
body: <p>I have a collectionview with 3 sections, but there is no item in first section, when i'm using </p>
  
  <pre><code>let indexPath = IndexPath(row: row, section: section)
  </code></pre>
  
  <p>the project will crash, so what should i input when there is no items for this, is there any function like </p>
  
  <pre><code>let indexPath = IndexPath(section: section)
  </code></pre>