R1:f0be29649da5

Fix a f()[0] use in rPd45855e33e0b98d521ea3e44a4c1f718821ec6cc

Summary: See D3291.

Test Plan: Ran `phpast.getast` via API.

Reviewers: alanh

Reviewed By: alanh

CC: aran

Differential Revision: https://secure.phabricator.com/D3292