Fix NotificationPanel animation jank.

Bug: 162599873
Bug: 161172460
Test: Manual -- To repro the bug, swipe on the Notification cards in the
closing direction. This should not in fact close the Notification Panel
since the user's intent is to scroll the Notification cards, not to
close the Notification panel. This also results in the animation jank.
This behavior is no longer observed after this fix.

Change-Id: I6144c064faf151a091ec66df4616036bf765e9fb