Fix issue where notifications remained hidden on lock screen after two quick power presses.

Tested at ToT and can't reproduce either the missing notifications, or the b/184396499 issue where the shade's notifications would be missing after allowing the phone to timeout and then using fingerprint bypass.

Fixes: 184028145
Bug: 184396499
Test: press power to lock and press it again quickly to cancel
Test: allow screen to timeout, then bypass using fingerprint
Change-Id: I3aa2ac74a1cf90a400cb7240453ee2af0015556e