Description:
------------
RecursiveIteratorIterator fails to Recurse into class implementing iteratorAggregate and returning RecursiveArrayIterator on private data. See test script.

Test script:
---------------
class X implements IteratorAggregate {
  private $data = ['X', 'X', 'X'];
  # public $data = ['X', 'X', 'X'];
  
  public function __construct($data = null) {
    $this->data = isset($data) ? $data : $this->data;
  }
  
  public function getIterator() {
    return new RecursiveArrayIterator($this->data);
  }
}

$x = new X([1, 2, new X(), 5]);
$it = new RecursiveIteratorIterator($x);
foreach($it as $v) {
  var_dump($v);
}

Expected result:
----------------
Expecting no difference between public and private data. RecursiveArrayIterator should make a copy of the private data on construction.