Merge pull request #4884 from mrj001/Issue4883

Fixed returns value; Issue 4883

src/Avalonia.Controls/ItemsControl.cs

@@ -169,7 +169,7 @@ namespace Avalonia.Controls
         /// </summary>
         /// <param name="items">The collection.</param>
         /// <param name="index">The index.</param>
-        /// <returns>The index of the item or -1 if the item was not found.</returns>
+        /// <returns>The item at the given index or null if the index is out of bounds.</returns>
         protected static object ElementAt(IEnumerable items, int index)
         {
             if (index != -1 && index < items.Count())