Description:
------------
When I load XML with fourth attribute of simplexml_load_file or simplexml_load_string, attributes are invisible. It's irrelevant if namespace is default (xmlns=) or prefixed (xmlns:x=).

Reproduce code:
---------------
$text = '<a xmlns="http://example.org"><c a="d">test</c></a>';
$xml = simplexml_load_string($text, null, 0, "http://example.org");
var_dump($xml->c["a"]);


Expected result:
----------------
object(SimpleXMLElement)#4 (1) {
  [0]=>
  string(1) "d"
}

Actual result:
--------------
NULL