Fix disappearing notifications when closing fullscreen QS

We might be setting alpha to 0 for wakeup-related events at that point.
Let's not do that when shade is open. This change adds a keyguard check

Bug: 189313235
Test: manual
Change-Id: Ibc73f71d31f3b10714a9c7ce4bb9a121e497ed5b
(cherry picked from commit cc8afa6b)