Do not assert if KIO::rawErrorDetail() is given a URL with no scheme
If the 'reqUrl' points to a URL that is not null but has no scheme, e.g. QUrl("foo"), then QUrl takes it as as a valid relative URL. However, the blank scheme is passed to KProtocolInfo::protocolClass() which asserts.
This can be triggered by, e.g. "konqueror --part webenginepart foo" where the "foo" generates a relative URL.
Check that the scheme is not empty before calling protocolClass().