Reset the flag of attaching nav to app to prevent flickering

The restoreNavigationBarFromApp() could now be called twice in live tile
mode. Reset the mNavigationBarAttachedToApp once the nav bar is detached
to prevent the nav fade-in animation playing twice.

Bug: 189900722
Test: atest RecentsAnimationControllerTest
Change-Id: Ifa02a7355d6503399de636646d73b9a4b6766a51