Prevent nullPointerException by updateBondedBluetoothDevices

In some very rare cases difficult to identify, it seems that the
IBluetooth.getBondedDevices() returns a Set with a null element.

This patch will prevent calling getBondState() if the device is null to
avoid a nullPointerException.

Change-Id: I9bcad60c37e03c77ec39227e5c947c002a3ae2c7