message: Try to check cent,z bin
diff: @@ -720,7 +720,7 @@ Bool_t AliAnalysisTaskXi1530::GoodTracksSelection() {
  tracklist* etl;
  eventpool* ep;
  // Event mixing pool
  - if (fsetmixing) {
  + if ( (centbin >= 0) && (zbin >= 0) && fsetmixing) {
  ep = &fEMpool[centbin][zbin];
  ep->push_back(tracklist());
  etl = &(ep->back());
  @@ -1797,7 +1797,7 @@ void AliAnalysisTaskXi1530::FillTracks() {
  }
  // Event Mixing
  - if (fsetmixing) {
  + if ((centbin >= 0) && (zbin >= 0) && fsetmixing) {
  eventpool& ep = fEMpool[centbin][zbin];
  int epsize = ep.size();
  if (epsize < (int)fnMix)
  @@ -2373,7 +2373,7 @@ void AliAnalysisTaskXi1530::FillTracksAOD() {
  }
  // Event Mixing
  - if (fsetmixing) {
  + if ((centbin >= 0) && (zbin >= 0) && fsetmixing) {
  eventpool& ep = fEMpool[centbin][zbin];
  int epsize = ep.size();
  if (epsize < (int)fnMix)
  