Fixed Peak/Scan list not updating when hidden in the background

[Mailaender]

Closes #912

[eselmeister]

Looks good. I would additionally recommend to check with instanceof if the object is a chromatogram selection:

@Override
public boolean setFocus() {

	DataUpdateSupport dataUpdateSupport = Activator.getDefault().getDataUpdateSupport();
	List<Object> objects = dataUpdateSupport.getUpdates(IChemClipseEvents.TOPIC_CHROMATOGRAM_XXD_UPDATE_SELECTION);
	if(!objects.isEmpty() && objects.get(0) instanceof IChromatogramSelection) {
		chromatogramSelection = (IChromatogramSelection)objects.get(0);
	}
	updateChromatogramSelection();
	return true;
}

[Mailaender]

Added the missing check.