Bass: Remove unnecessary creation of active syncHandle lists

Check directly for the existence of a syncHandle in
getActiveSyncedSources instead of creating a new list if it's
not modified or used multiple times.

Bug: 390189678
Flag: EXEMPT, refactor no-op
Test: atest BassClientServiceTest
Change-Id: I5b19cac95474da208037db5eb167b84e2d86aa15