Fix another qsprintf() straggler in "Has Open Subtasks"
Summary: See https://discourse.phabricator-community.org/t/error-message-is-not-being-logged-when-unable-to-connect-to-the-database/2201/.
Test Plan: Queried for "With Open Subtasks" and "With No Open Subtasks".
Reviewers: amckinley, joshuaspence
Reviewed By: joshuaspence
Subscribers: joshuaspence
Differential Revision: https://secure.phabricator.com/D19880