Fix tag limit logic in PHUIHandleTagListView

Summary: Fixes T10648. This was goofed and always did a meaningless no-op slice -- I mucked it up while doing the disabled project stuff elsewhere.

Test Plan:

• Tagged something with 5 projects.
• Saw the list sliced to 4 (the limit) with "...".

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10648

Differential Revision: https://secure.phabricator.com/D15508