title: DiffUtils do not display new items
body: <p><code>DiffUtils.dispatchUpdatesTo(adapter)</code> not updating the size of my array in <code>recyclerView</code></p>
  
  <p>my <code>result</code> has size more than current <code>itemList</code>, but displays only current size</p>
  
  <p>How to display changes in size of my array by <code>DiffUtils</code> ? I think use <code>notifyDatasetChanged()</code> is not correct. </p>
  
  <p>Here's how i do this now in adapter:</p>
  
  <pre><code>    fun update(items: List&lt;ITEM&gt;) {
      updateAdapterWithDiffResult(calculateDiff(items))
  }
  
  private fun updateAdapterWithDiffResult(result: DiffUtil.DiffResult) {
      result.dispatchUpdatesTo(this)
  }
  
  private fun calculateDiff(newItems: List&lt;ITEM&gt;) =
          DiffUtil.calculateDiff(DiffUtilCallback(itemList, newItems))
  </code></pre>