PileUpMT: Print event range read failure occurs in

I've seen segfaults in MT pileup digitization (and intermittent segfaults have been reported in ART tests, e.g. ATLASSIM-6459, ATLASSIM-6491, ATLASSIM-6479).

It looks like these are caused by intermittent I/O issues when reading in minimum bias events. This MR is supposed to help debug this by printing the run and event numbers of the minbias events that may have been corrupted while being read in.

From my preliminary investigation, the problem seems to be somewhat alleviated by reading in the batches of minbias events at once when they are loaded, rather than allowing StoreGate to load the necessary parts of those events on demand. Nevertheless, this doesn't seem to completely fix the problem, particularly at high mu.