R1:2b6935351987

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