Fixes encoding issues when parsing WSDL files

This change solves the encoding issues described in the following two posts. Issue since SoapUI 4.6.4

https://forum.soapui.org/viewtopic.php?f=13&t=22976
http://forum.soapui.org/viewtopic.php?f=13&t=22911

I tested it with two file encodings by setting 
-Dfile.encoding=UTF-8
-Dfile.encoding=windows-1252

and importing
https://service-es.bygogmiljoe.dk/Sagsbehandling.svc?singleWsdl
http://forum.soapui.org/download/file.php?id=3031&sid=1029232716ee9278136461950819c392 (SecurityTokenService)

The next branch (5.0) is impacted by the same issue.