Handle missing Hlt2 SelReports in Tesla

Occasionally, HLT2 did not write Hlt2/SelReports for very busy events. Previously, the TeslaReportAlgo was skipping such events happily.

Here we restore this behaviour, such that if Hlt2/SelReports cannot be decoded, no event is written out.

This was spotted in the validation productions, see https://lblogbook.cern.ch/Operations/27130