SystemUI: fix small jump when expanding QS w/o notifications

When expanding with two fingers, or one finger quick-setting pull down,
the disappearing "No notifications" animation would cause some jumpiness
without this.

Change-Id: I71881a86df217cedc8b8bc648b2e9d389aeb6cdd
Signed-off-by: Roman Birg <roman@cyngn.com>