Set user if it doesn't exist in updateCurrentUser
Set user if it doesn't exist in updateCurrentUser

Coming directly from the /join form (since we aren't doing a full page
reload) there is no `user` in the store. This just sets the user with
the response if it doesn't previously exist. If the user does it exist
it just continues as it did before.

ello/webapp,ello/webapp,ello/webapp