Fix Maniphest Next button not working when default query has 100+ results.

Summary: If there is no /query in the URL, the default query would be lost when clicking Next, causing the search form to be shown on the second page. This is not so likely to happen on a standard Phabricator installation because the default query is Assigned, and few people will have 100+ tasks assigned.

Test Plan:
* Go to /maniphest/query/edit/
* Move Open Tasks to the top
* Go to /maniphest/
* Click Next on the bottom right
* See only tasks that are actually open

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7667