LinkResolver::resolve_field resolved_klass cannot be null

There's a case for throwing NSFE in linkResolver that is impossible since resolved_klass can't be null.

The name is misleading. It's not really the declared class owner of the field, it's the referenced class, but it is resolved with klass_at.

                getstatic Field x:"LMyClass;";

   // resolve klass
  _resolved_klass = pool->klass_ref_at(index, CHECK);

We usually refer to this as REFC.