[PWGCF] Updating the channel mirroring logic and adding an option to fill histograms run by run

[MartijnLaarhoven]

Updating the channel mirroring logic and adding an option to fill histograms run by run

[Copilot]

Pull request overview

This PR adjusts FT0 channel gain-equalization indexing within the long-range dihadron correlation task, aligning the correction factor lookup with the FT0 channel ID used throughout the histogramming/mirroring logic.

Changes:

• Update FT0 amplitude gain correction to index cstFT0RelGain by id (channel ID) instead of iCh (loop index), for both FT0A and FT0C.

Comments suppressed due to low confidence (2)

PWGCF/TwoParticleCorrelations/Tasks/longRangeDihadronCor.cxx:695

• histAmpCorrectPerRun[lastRunNumber]->Fill(...) is executed whenever system == SameEvent, even when cfgRunbyRunAmplitudeFT0 is false (in that case lastRunNumber stays -1 and the map entry will be missing/null, leading to a crash via operator[] inserting a null shared_ptr). Guard this fill with cfgRunbyRunAmplitudeFT0 and use find() (no operator[]) to ensure the histogram exists before calling Fill().

      if (system == SameEvent) {
        registry.fill(HIST("FT0AmpCorrect"), id, ampl);
        histAmpCorrectPerRun[lastRunNumber]->Fill(id, ampl);
      }

PWGCF/TwoParticleCorrelations/Tasks/longRangeDihadronCor.cxx:707

• Same issue as above: histAmpCorrectPerRun[lastRunNumber]->Fill(...) can dereference a null shared_ptr when run-by-run histograms are disabled or not created for the run (because operator[] inserts a default/null entry). Please guard with cfgRunbyRunAmplitudeFT0 and lookup with find() before filling.

      if (system == SameEvent) {
        registry.fill(HIST("FT0AmpCorrect"), id, ampl);
        histAmpCorrectPerRun[lastRunNumber]->Fill(id, ampl);
      }

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