AudioDeviceInventory: protect from null BT identity address

It is possible that the address returned by BluetoothDevice.getIdentityAddress()
is null in which case AudioDeviceInventory.onUpdateLeAudioGroupAddresses() must prevent
from setting @NonNull DeviceInfo fields mDeviceIdentityAddress and mPeerIdentityDeviceAddress
to null.

Bug: 334973381
Test: repro steps in bug.
Change-Id: Ib3b4693df4abf22774803c9aac60f532cd9f6a72