AdapterProperties: Guard unregisterReceiver

At first boot if Bluetooth is not enabled by default the Bluetooth app
will crash due to a poorly guarded cleanup method.

The root cause is that BluetoothMangerService.handleOnBootPhase() issues
a MESSAGE_GET_NAME_AND_ADDRESS, which inturn will try get device address
and name. When done it will call unbindAndFinish() if Bluetooth is not
enabled. The Bluetooth app then cleans up in preparation for shutdown
and the crash occurs.

Test: def_bluetooth_on => false in SettingsProvider defaults. Build/boot
Change-Id: Idc6817eacd75fcc22d284ca0e54933914b587e49