Fix an incorrectly spelled call on the registration error pathway

Summary: If you copy the registration URL, then register, then load the URL again while logged out (i.e., attempt to reuse the registration URL), we try to show you a tailored error message. However, this call is not correct so we show you a not-so tailored exception instead.

Test Plan:
  - Get to the registration screen.
  - Save URL.
  - Complete registration.
  - Log out.
  - Return to saved URL.

Previously, exception. Now, readable error.

{F117585}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D8322