R1:4e41e164e5f1

Skip captcha when redeeming an invite

Summary: This wasn't actually being skipped for invites; really skip it.

Test Plan:
- Registered without invite, captcha.
- Registered with invite, no captcha.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11877