Bass: Prevent adding already synced broadcast in addSelectSourceRequest

addSelectSourceRequest adds operations to the queue, which later is
processed by handleSelectSourceRequest.

handleSelectSourceRequest already filtered out operations on already
synced broadcast.

This CL prevent adding already synced broadcast to the queue to avoid
additional operation of adding and retrieving from queue.

It can be observed in scenario when an unintentional paused sink is
triggered by a music pause while the remote unsyncs from BIS and PA.
Subsequently, addSelectSourceRequest is called on every onScanResult,
even if the source is already synced.

Bug: 390189678
Flag: EXEMPT, regression covered by unit tests
Test: atest BassClientServiceTest
Change-Id: I8056a9ae048e52a87b3bd15e3ef60799d7edcea4