Plot RoI map for the first leg only in multi-leg triggers [ATR-26626]
If we have a multipe-leg trigger, the monitoring RoI map should look at the first leg only, so that a HLT_eX_tauX chain would only produce an entry in the electron RoI map.
This fixes ATR-26626.
While the original problem (that the jet RoI map is non-empty) is rare, the fix should reduce the RoI multiplicity in a way that is noticeable even in few events, as suggested by @tamartin .
I have checked this on the AOD from 23.0/Athena/x86_64-centos7-gcc11-opt/2023-08-30T2101/TrigAnalysisTest/test_trigAna_RDOtoRun3DQ_v1Dev_build/ (20 events) and the RoI map event count reduced compared with the out-of-box test:
HLT_MuonsRoIs 640 -> 577
HLT_ElectronsRoIs: 659 -> 648
While this change is in no way urgent, it would be nice to have it in as soon as possible.