Fix a bug with T1643

Summary: The construct count(x == 0) should be count(x) == 0. This causes a concrete problem because count(0) is 1.

Test Plan: eyeballed it~

Reviewers: btrahan, vrana, klimek

Reviewed By: klimek

CC: aran

Maniphest Tasks: T1643

Differential Revision: https://secure.phabricator.com/D4060