added condition on ambi tracks loop to avoid crashes

added condition on ambi tracks loop to avoid crashes (in particular, for some Pb-Pb MC)

Author: altsybee

DPG/Tasks/AOTEvent/eventSelectionQa.cxx

@@ -1000,17 +1000,19 @@ struct EventSelectionQaTask {
       auto mapAmbTrIdsIt = mapAmbTrIds.find(track.globalIndex());
       int ambTrId = mapAmbTrIdsIt == mapAmbTrIds.end() ? -1 : mapAmbTrIdsIt->second;
       int indexBc = ambTrId < 0 ? track.collision_as<ColEvSels>().bc_as<BCsRun3>().globalIndex() : ambTracks.iteratorAt(ambTrId).bc_as<BCsRun3>().begin().globalIndex();
-      auto bc = bcs.iteratorAt(indexBc);
-      int64_t globalBC = bc.globalBC() + floor(track.trackTime() / o2::constants::lhc::LHCBunchSpacingNS);
+      if (ambTrId < 0) { // temprorary limitation, to avoid crashes, in particular, on MC Pb-Pb datasets
+        auto bc = bcs.iteratorAt(indexBc);
+        int64_t globalBC = bc.globalBC() + floor(track.trackTime() / o2::constants::lhc::LHCBunchSpacingNS);
 
-      int32_t indexClosestTVX = findClosest(globalBC, mapGlobalBcWithTVX);
-      int bcDiff = static_cast<int>(globalBC - vGlobalBCs[indexClosestTVX]);
-      if (track.hasTOF() || track.hasTRD() || !track.hasITS() || !track.hasTPC() || track.pt() < 1)
-        continue;
-      histos.fill(HIST("hTrackBcDiffVsEtaAll"), track.eta(), bcDiff);
-      if (track.eta() < -0.2 || track.eta() > 0.2)
-        continue;
-      histos.fill(HIST("hSecondsTVXvsBcDifAll"), bc.timestamp() / 1000., bcDiff);
+        int32_t indexClosestTVX = findClosest(globalBC, mapGlobalBcWithTVX);
+        int bcDiff = static_cast<int>(globalBC - vGlobalBCs[indexClosestTVX]);
+        if (track.hasTOF() || track.hasTRD() || !track.hasITS() || !track.hasTPC() || track.pt() < 1)
+          continue;
+        histos.fill(HIST("hTrackBcDiffVsEtaAll"), track.eta(), bcDiff);
+        if (track.eta() < -0.2 || track.eta() > 0.2)
+          continue;
+        histos.fill(HIST("hSecondsTVXvsBcDifAll"), bc.timestamp() / 1000., bcDiff);
+      }
     }
 
     // collision-based event selection qa