Restore process working directory at end of performXMLCheck() to fix issue #179

[dean-e-peterson]

Attempt to fix issue #179, where a directory containing an xml file cannot be renamed or deleted after editing a contained XML file. Fix by restoring the working directory to its previous state.

Known limitations:

• Written by a non-C/C++ developer, so string handling or something else may be wrong.
• Does not address any other locations where the process working directory is changed with _wchdir(), such as in XmlValidation().
• (Edit) Also does not handle if anything after the end of the method requires the process working directory to remain changed.