Description:
------------
ParentIterator that only shows those elements which have children.
But I can't get the expected result without rewind() in starting an iteration.

Reproduce code:
---------------
$target = array(
    'foo' => array(1,2,3),
    'bar' => array(11,12,13),
    'baz'
);
$rai = new RecursiveArrayIterator($target);
$pi = new ParentIterator($rai);
//$pi->rewind();
while ($pi->valid()) {
    var_dump($pi->current());
    $pi->next();
}

Expected result:
----------------
array(5) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}
array(5) {
  [0]=>
  int(11)
  [1]=>
  int(12)
  [2]=>
  int(13)
}

Actual result:
--------------
// no output