NPE in BluetoothDevice.fetchUuidsWithSdp

This is caused by access fetchUuidsWithSdp after bluetooth is turned off.
We can add check null pointer for sService,
before call sService.fetchRemoteUuids(this) to fix this problem;

bug:12533948
Change-Id: Id2cab92a56185073fabcabcfb21a243e99a60cee