Consider lock icon when determining minimum top padding.

Otherwise, the clock will be able to overlap with the lock icon in some
situations. A side effect of this change is that only 2 notifications
will be displayed when the now playing indication is present.

Fixes: 131311937
Test: manual - need three visible notifs + now playing indication
Change-Id: Ieffa97bc20a45fb82fb258deca7c1f289b0ce003