Don't bail on no effect exception

Summary: The main reason for this is to not exit with 1 when no paths are lintable (which is more success than failure).

Test Plan:
Returned empty array from `buildLinters()`, then:

  $ arc lint
  $ echo $? # 0

Reviewers: epriestley

Reviewed By: epriestley

CC: wez, aran, Korvin

Differential Revision: https://secure.phabricator.com/D4625