Fixes crash when tap on nav bar without using quickstep

Fixes crash on nav bar by setting default pos/states of home button and
track opacity to avoid null error when tapping the nav bar before using
quick scrub. Also fixes the lack of animation of quick scrub when it
retracts.

Fixes: 73814434
Test: tap the nav bar upon reboot (or kill sysui process) before using
quickscrub

Change-Id: I2d35dcdf6e860ffb3959d48b4a4cdc319e939d1b