Cancel show runnable when bouncer is hidden

Otherwise the bouncer might report "showing soon" and future
show() calls will be aborted.

Test: swipe up and down, wait for face, swipe up
Test: tap on notification on bouncer
Test: swipe up, unlock from bouncer
Test: unlock on lock screen, swipe up to dismiss bouncer
Fixes: 132846921
Change-Id: I22a1af2ef903b266ae8d8fcb9eb55f6cc11aeae2
(cherry picked from commit 9b8e5e38)