Since D101206 (`ba79fb2e1ff7130cde02fbbd325f0f96f8a522ca`) the `__hash_node::__value_`
member is wrapped in an anonymous union. `ValueObject::GetChildMemberWithName` doesn't see
through the union.
This patch accounts for this possible new layout by getting a handle to
the union before doing the by-name `__value_` lookup.