Fix setContentAlpha skipping all TaskViews when runningTaskId is -1

- Currently when runningTaskId is -1, it can skips setting contentAlpha for all TaskViews if they haven't been loaded, this cause RecentsView to become empty in the bug
- Can be reproduced with excludeFromRecents=true apps

Bug: 324495241
Test: swipe up from an app that has excludeFromRecents=true, e.g.
Volume Dialog, Home quick settings tile, and Routines widget; ensure RecentsView is visible after gesture settles
Flag: None

Change-Id: I9f1b4ffed6d09805c83c6e2241903c73d4ead9ad