message: Fix in initialization of last particle in the stack, needed for the separate simulation of trigger event
  I apparently cannot approve with "+1", I am merging directly (the tests passed already).
diff: @@ -221,7 +221,10 @@ void AliGenPileup::Generate()
  // Loop over the generated collision times, call the generator
  // and correct the partcile times in the stack
  AliStack *stack = AliRunLoader::Instance()->Stack();
  - Int_t lastpart=0;
  + Int_t lastpart=stack->GetNprimary();
  + // NOTE: the initialization of lastpart accounts for particles that could
  + // be already present in the stack from another generator
  + // (e.g. in the case of separate simulation of the trigger event)
  entry->SetFirst(lastpart);
  // Take the diamond from gAlice and set it in AliGenPileup
  // Needed in the case of simulations with a cocktail of trigger event + AliGenPileup
  