Fix for Mini2

[Auday]

To make the demo work on Mini2, we need to add the code below to func setupVideoPreviewer() before DJIVideoPreviewer.instance().start()

        if (product!.model!.isEqual( DJIAircraftModelNameDJIMini2 ))
        {
            DJIVideoPreviewer.instance()?.encoderType = H264EncoderType._DJIMini2 
        }