Handling of missing data: show at least available data

[smarr]

Currently, we simply say when a benchmark is missing from one of the data sets.
It would be more useful, if we at least show the data for the current set.
Of course, no diff values, but at least the mean run time etc for the change set, if the data is available. I think it will need to be the change set, to be consistent with the other values.