Description:
------------
If autocreating new nodes by id ($obj->node[0] = '') 
SimpleXML doesn't assign value to first node. Creating 
first node w/o using id works fine.

Reproduce code:
---------------
<?php

  $sx1 = new SimpleXMLElement("<root />");

  $sx1->node[0] = 'node1';
  $sx1->node[1] = 'node2';

?>

Expected result:
----------------
object(SimpleXMLElement)[1]
  public 'node' => 
    array
      0 => 'node1' (length=5)
      1 => 'node2' (length=5)

Actual result:
--------------
object(SimpleXMLElement)[1]
  public 'node' => 
    array
      0 => 
        object(SimpleXMLElement)[6]
      1 => 'node2' (length=5)