NPE on Android when stopping scanning and the Bluetooth adapter has gone

[blackspherefollower]

Describe the bug
From sentry:

NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.stopScan(android.bluetooth.le.ScanCallback)' on a null object reference

I suspect that the unchecked results in https://github.com/deviceplug/btleplug/blob/master/src/droidplug/java/src/main/java/com/nonpolynomial/btleplug/android/impl/Adapter.java#L39 are to blame (it's probably safe to ignore NULL results, as that suggests the Bluetooth adapter has gone away and hence the scan has already stopped).

Whilst I can't reproduce this, the reporter stated that they had Bluetooth disabled on their phone when they experienced the crash (Android 10 running on an LG K50S)