request.client may be null

[ronag]

The spec says that request.client may be null.

A request has an associated client (null or an environment settings object).

However, the spec does not take this into account in some parts of the spec, e.g.

8. If request’s window is "client", then set request’s window to request’s
   client, if request’s client’s global object is a Window object; otherwise
   "no-window".

9. If request’s origin is "client", then set request’s origin to request’s
   client’s origin.