Task thumbnail background is spilling to the front, making the BK 1px smaller to fix it

This change ag/17003268 was meant as a solution for b/146521490 but
it's ineficient so this other solution is simpler and more performant.

This solution only makes the background 1px smaller and that prevents
it from spilling in the Anti Aliasing.

Test: Put Telegram in recent Task (shouldn't be the first one) and you won't see a white border. Also when a task was in multitask the backgroudn should be draw.
Fix: 223761979
Change-Id: I6855e9ecce1e06f7a9311c62a038d34b04fe2398