Foreign-Key Join creates an invalid topology

Foreign-Key Join results are not required to be materialized by default, but they might be needed if downstream operators need to perform lookups on the result (such as when the join result participates in an equi-join).

Currently, if the result is explicitly materialized (via Materialized), this works correctly, but if the result is not materialized explicitly, but is needed, the topology builder throws an exception that the result store isn't added to the topology. This was an oversight in testing and review and needs to be fixed ASAP.