FindDescriptor with Link Block Errors out

[ifadams]

Describe the bug
A FindDescriptor call with an included link block returns an error about non-unique returns

To Reproduce

Add a descriptor with a valid link to an existing metadata entity.

Then issue a find descriptor call, using a combination of FindEntity and Link, and use the affiliated link block with the FindDescriptor call, for example (in python)

    constraints = {"name": ["==", "Jane Doe"]}
    find_entity_q = query_helpers.find_entity("person", constraints=constraints, ref_tag=1234)

    link = query_helpers.create_link(1234)

    desc_find = {}
    desc_find["set"] = "pretty_faces"
    constraints = {"linked_prop": ["==",50]}
    desc_find["results"] = {"list": ["linked_prop"]}
    desc_find["link"] = link
    desc_find["constraints"] = constraints

    query_desc = {}
    query_desc["FindDescriptor"] = desc_find

    trans.append(find_entity_q)
    trans.append(query_desc)

Expected behavior

We should have the relevant descriptors linked to the specified FindEntity and their properties returned.

[ifadams]

The source of this error appears to be an accidental setting of the unique flag when querying against the descriptor set internally.