handle missing clusters in AsgPtEtaSelectionTool
Some derivations strip un-needed e-gamma clusters from the file, causing the existing code to fail/crash. This now prints a warning/error instead and adds another cut for the cluster being present.
The warning/error is mostly so you catch it if this is not the intended behavior. If it is, you can turn it off.
Not sure this is the best/correct thing to do, but it ought to be better than what we have now.