Fix rendering of offset-paged query panels including "Notifications"
Summary:
See <https://discourse.phabricator-community.org/t/call-to-undefined-method-phuipagerview-gethasmoreresults-in-2019-week-13/2586/>.
A small number of queries (including "Notifications" and (global) "Search") use offset-based pagers which have a slightly different API `PHUIPagerView` instead of `AphrontCursorPagerView`. This leads to a fatal in the new code for the "View All Results" buttons.
To fix this, just do an `instanceof` test. Some day we can unify the pagers.
Test Plan: Added a notifications panel, rendered it, saw it work instead of fataling on "getHasMoreResults()". Also rendered some normal panels.
Reviewers: amckinley
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20366