Don't do string concatenation in queryfx_all()

Summary: Searching for image macros was broken, and this fixes it.

Test Plan: load /macro/?name=test - the page loads instead of throwing an exception

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4658