Pull request for Issue867: IDEASXASScanConfigurationView ROI warning ignores selected detector 

Issue #867

It was working, but just wasn't updating the label when a new detector was selected.  Updating when a new detector is selected caused it to crash when selecting "none" because it tried to access none's ROIs to update the label.  Added a check to avoid that.

Altered:
```IDEASXASScanConfigurationView``` to call ```onROIChange()``` when the
detector choice has been changed.

Altered:
```IDEASXASScanConfigurationView::onROIChange``` to check if 'none' is
selected for the current XRF detector before trying to access the set
ROIs for it.