Fix exempt vs unexempt scheduled sync standby bucket logic

Fix for bug in AppStandbyController that would treat all scheduled
syncs for user 0 as unexempted syncs and syncs for not user 0 as
exempted syncs, regardless of the actual exemption status.

Fixes: 150016258
Test: atest AppStandbyControllerTests

Change-Id: Ie9e63c2954d0abe2a28469ea95ba6995a5c8696d
(cherry picked from commit 3ffa92f6)