SI-7475 Address review comments in FindMembers

  - comment the cases in `isNewMember`
  - check both sides for privacy (doesn't influence behaviour of
    any tests, but it means that method can be understood without
    understanding the order of traversal of members.)
  - hoist `findAll`
  - break out of the loop in `FindMembers` as soon as we determine
    that the candidate member is matched by an already-found member
    and can be discarded.