Description:
------------
When an XML file has an empty element defined as xs:token in XSD, and it is loaded into a DOMDocument and then schemaValidate is called, the server CPU begins to race and content is never returned to browser.

The W3C definition of xs:token does not prohibit empty xs:token elements.  



Reproduce code:
---------------
$aDOM = new DOMDocument("1.0");
$aDOM->load("file.xml");
$aDOM->schemaValidate("file.xsd");

XML File:

<?xml version="1.0"?>
<people>
     <person>
         <fname>John</fname>
         <mname/>
         <lname>Doe</lname>
     </person>
</people>

XSD File:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="people">
     <xs:complexType>
         <xs:sequence>
             <xs:element name="person" type="persontype" minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence>
     </xs:complexType>
</xs:element>

<xs:complexType name="persontype">
     <xs:sequence>
         <xs:element name="fname" type="xs:token"/>
         <xs:element name="mfname" type="xs:token"/>
         <xs:element name="lfname" type="xs:token"/>
     </xs:sequence>
</xs:complexType>

</xs:schema>


Expected result:
----------------
schemaValidate should return true.

Actual result:
--------------
CPU races, server does not return content to browser.