web/requestURI: add undefined xhr.channel guard
web/requestURI: add undefined xhr.channel guard

redaktor/rdflib.js,timbl/rdflib.js,timbl/rdflib.js,ariutta/rdflib.js,timbl/rdflib.js,ariutta/rdflib.js,redaktor/rdflib.js,nicola/rdflib.js,ariutta/rdflib.js,nicola/rdflib.js