Correctly clip QS during heads-up pull down

Test: pull down heads-up
Test: swipe-up heads-up
Test: receive hun, wait for timeout
Test: atest NotificationShadeDepthControllerTest
Test: atest NotificationPanelViewControllerTest
Fixes: 197641911
Change-Id: I47914698091aedfe7e4b1004039467de197194c7