dkimitsa: this is very special workaround for bug #336
it happens when didReceiveAuthenticationChallenge navigation delegate's
callback being called and challenge is instance of WKNSURLAuthenticationChallenge class
the issue here is that WKNSURLAuthenticationChallenge itself doesn't inherit
NSURLAuthenticationChallenge and RoboVM can't build java object for it as it is not known
and hangs with exception.