#333 generateXPCML fails if doc was serialized

[kakster99]

the generateXPCML method fails if the ProgramCallDocument instance was constructed from serialized PCML document.
NullPointerException in PcmlDocNode.getAttributeValue(String) due to m_XmlAttrs being null
The intention for calling generateXPCML from our perspective is for debugging purposes - e.g., if program call throws exception we would like to capture the contents of the Pcml Document and write to our error logs. Also, if we have debug level logging enabled in our application we would like to dump the contents before and after the program call.
If we construct our ProgramCallDocument from a filename and the file is non-serialized PCML, the above works fine, but if we construct from a filename or an InputStream with serialized PCML we get the above NullPointerException.