FOR XEP-0045: 10.4 Revoking Owner Status

* A service MUST NOT allow an owner to revoke his or her own owner
  status if there are no other owners; if an owner attempts to do this,
  the service MUST return a <conflict/> error to the owner. However, a
  service SHOULD allow an owner to revoke his or her own owner status if
  there are other owners.
Fixing affiliation reason reset when empty