XML Handler

A number of issues with the XML functions in the state environment.

- Successive "RemoveAttribute" calls result in:
"
Exception thrown: read access violation.
**this** was 0x68.
"
- SaveToString calls once an attribute has been removed and then added throws the same error
- SaveToString calls can duplicate "xmlns=..."

This error can be repeated by including an XML file in the resource folder and using this code:

auto xml_string = pStateEnvironment->LoadResourceString("test");
auto xml_object = pStateEnvironment->ParseXMLString(xml_string);
auto xml_string_back = xml_object->SaveToString(false);

Start by reproducing the report with an XML resource and the LoadResourceString, ParseXMLString, RemoveAttribute, and SaveToString calls shown in the issue. Trace successive attribute removal and remove-then-add serialization, then verify that SaveToString no longer crashes and does not duplicate xmlns entries.

Written by the indexing model from the issue text.