Make siClusterMap a local variable - avoid interference from multiple execute() calls
m_siClusterMap
was causing crashes when running e.g.
athena.py --stdcmalloc --threads 8 --concurrent-events 4 --filesInput /cvmfs/atlas-nightlies.cern.ch/repo/data/data-art/TrigP1Test/data18_13TeV.00360026.physics_EnhancedBias.merge.RAW._lb0151._SFO-1._0001.1 --skipEvents 0 -c 'doEmptyMenu=True;doMuonSlice=True;doWriteBS=False;doWriteRDOTrigger=False;forceEnableAllChains=True' TriggerJobOpts/runHLT_standalone.py
Work towards ATR-20227.