Description:
------------
The SDO fails to read a file with repeated nill elements when the type is and extension of a simple type. This has been reported in Tuscany as https://issues.apache.org/jira/browse/TUSCANY-2041

Reproduce code:
---------------
With the schema

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        targetNamespace="http://www.example.org/AnnonTypes"
        xmlns:tns="http://www.example.org/AnnonTypes" elementFormDefault="qualified">
        
        <element name="Top">
          <complexType>
            <sequence>
<element name="attribute" nillable="true" minOccurs="0" maxOccurs="unbounded">
<complexType>
<simpleContent>
<extension base="string">
<attribute name="name" type="string" use="required"/>
</extension>
</simpleContent>
</complexType>
</element>
            </sequence>
          </complexType>
        </element>
</schema>

And XML

<tns:Top xmlns:tns="http://www.example.org/AnnonTypes"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.example.org/AnnonTypes AnnonTypes2.xsd ">
  
  <tns:attribute name="ABC" xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
  <!--tns:attribute name="DEF" xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
  <tns:attribute name="GHI" xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
  <tns:attribute name="JKL" xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"-->
</tns:Top>



Expected result:
----------------
Successfully parsed input

Actual result:
--------------
When multiple attribute elements are present the following error is reported.

SDO_DAS_XML_ParserException Object
(
    [message:protected] => SDO_DAS_XML::loadFile - Unable to parse the supplied
xml file
1 parse error(s) occurred when parsing the file 'AnnonTypes2.xml':
1. Parser found unknown element attribute

    [string:private] =>
    [code:protected] => 0
    [file:protected] => C:\simon\php\workspace\php-branch\phpscripts\chrisdougla
s\test.php
    [line:protected] => 52
    [trace:private] => Array
        (
            [0] => Array
                (
                    [file] => C:\simon\php\workspace\php-branch\phpscripts\chris
douglas\test.php
                    [line] => 52
                    [function] => loadFile
                    [class] => SDO_DAS_XML
                    [type] => ->
                    [args] => Array
                        (
                            [0] => AnnonTypes2.xml
                        )

                )

        )

    [cause] =>
)