Fix malformed trace sections

In some scenarios, the following trace sections would never close:

 - "KeyguardViewMediator#handleShow"
 - "KeyguardViewMediator#handleStartKeyguardExitAnimation"

Test: Capture perfetto trace, inspect trace to verify all slices end
Flag: EXEMPT system tracing only
Change-Id: Ia3c92130672988449061167663f8faf33894f037