Underp ReleephDefaultFieldSelector

Summary: Oops.  Functions only return stuff when you call the `return()` function on the `lvalue`.

Test Plan: Use `ReleephDefaultFieldSelector` is the field selector in a test Releeph project.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5362