Add missing InvalidBluetoothAdapterError to QML discovery model

QBluetoothServiceDiscoveryAgent::InvalidBluetoothAdapter was introduced
by Qt 5.3 but never added to the QML BluetoothDiscoveryModel. This patch
fixes the problem.

This was noticed due to a crash on Android emulator.

Change-Id: I652576929659ca370216133154e36158e8425711
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>
Fix crash during service discovery on Android

This is caused when running a service discovery on an Android emulator.
The emulator does not have a local Bluetooth device despite the Qt code
assuming it.

Change-Id: I9c0d826d14e7494bfeb27d449f9b6f568860d917
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>