Fix: /data/circles: Do not return null docs
Fix: /data/circles: Do not return null docs

Check to see if a membership pertains to a
circle before returning it.

holmwell/circle-blvd,ellipsonic/circle-blvd,secret-project/circle-blvd,myersg86/circle-blvd,holmwell/circle-blvd,myersg86/circle-blvd,ellipsonic/circle-blvd,holmwell/circle-blvd,myersg86/circle-blvd,ellipsonic/circle-blvd,ellipsonic/circle-blvd,secret-project/circle-blvd,myersg86/circle-blvd,secret-project/circle-blvd,holmwell/circle-blvd,secret-project/circle-blvd