crashes on empty files

Currently people are running into segmentation violations when trying to process empty files (no CollectionTree).

It appears that this line https://gitlab.cern.ch/atlas-caf/CAFCore/blob/master/QFramework/Root/TQMultiChannelAnalysisSampleVisitor.cxx#L506 triggers the crash which is understandable. Parts of the processing here needs to be run even if there's no event in the file (due to meta data handling, e.g., cutBookKeeper extraction/merging for skimming).

The most confusing part (to me) is why this didn't happen earlier as the responsible line should have been in place already much earlier....

Tagging @mbasso as original reporter