rearranged user retrieval

invite_redeemer.rb

def invited_user
  @invited_user ||= get_invited_user
end

def get_invited_user
  result = get_existing_user
  result ||= create_new_user
  result.send_welcome_message = false
  result
end

def get_existing_user
  User.where(email: invite.email).first
end

def create_new_user
  User.create_for_email(invite.email, trust_level: SiteSetting.default_invitee_trust_level)
end