Added error message if an external XML document could not be loaded due to syntax errors
Added error message if an external XML document could not be loaded due to syntax errors

ariyapour/xml3d.js,xml3d/xml3d.js,Fiware/webui.Xml3d.js,ariyapour/xml3d.js,xml3d/xml3d.js,CCLDESTY/xml3d.js,Fiware/webui.Xml3d.js,CCLDESTY/xml3d.js