Debugged this with help from Darren:

Added:
- CLSSIS3820ScalerView::hasAmplifierView() ~ Function which returns
whether this view has a valid, non null amplifierView_

Altered:
- CLSSIS3820ScalerChannelView::setAmplifierViewFormat() and
setAmplifierViewPrecision() ~ not check if amplifierView_ is not null
before attempting to set its precision/format

- CLSSIS3820ScalerView::setAmplifierViewFormat() and
setAmplifierViewPrecision ~ in a belt and braces approach this also
checks whether the channel view has a valid amplifierView_ by calling
hasAmplifierView() before attempting to set its format/precision.