Fix calling method on the stopped service

Since the callback was scheduled on the main loop, the service can be
stopped after that and before the callback is called. We should check
if the service is still running before we execute the scheduled callback
logic.

Bug: 298898621
Test: atest BluetoothInstrumentationTests
Change-Id: Id7c9fa75758a13aea93d2d235feb99bfc4cda85c