Fix dashboard list if there are no results

Summary:
We'll fire a bad query if there are no dashboards in the result list, see:

http://pastie.org/private/j0f8tzbdahwragxjsk8qxq

Test Plan: Viewed result list with no dashboards.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10207