Missing catch for isHandleAvailable.check() in addPerson
isHandleAvailable.check() failure does not have its own catch. We are erroneously catching it as an invitation code failure and passing that to the person. Fix.
https://source.ind.ie/project/waystone/blob/master/routes/rest-api/post/addPerson.coffee#L90
(Part of the sprint to make Waystone sign-up process more robust.)