message: do not dump empty events
diff: @@ -718,7 +718,7 @@ void* AliHLTTPCCATrackerComponent::TrackerDoEvent(void* par)
  }
  }
  - if (fDumpEvent)
  + if (fDumpEvent && nClustersTotal)
  {
  static int nEvent = 0;
  std::ofstream out;
  