Fix URI construction of typeahead browse "more" pager

Summary: Ref T13251. See https://phabricator.wikimedia.org/T216849.

Test Plan:

• With more than 100 projects (or, set $limit = 3)...
• Edit a task, then click the "Browse" magnifying glass icon next to the "Tags" typeahead.
• Before change: fatal on 'q' being null.
• After change: no fatal.

Reviewers: amckinley, 20after4

Reviewed By: amckinley

Maniphest Tasks: T13251

Differential Revision: https://secure.phabricator.com/D20204