message: In case of embedding, recover the MCheader from external event
diff: #include "AliAODEvent.h"
  #include "AliGenEventHeader.h"
  #include "AliLog.h"
  +#include "AliAnalysisTaskEmcalEmbeddingHelper.h"
  /// \cond CLASSIMP
  ClassImp(AliCaloTrackAODReader) ;
  @@ -154,7 +155,13 @@ AliAODMCHeader* AliCaloTrackAODReader::GetAODMCHeader() const
  {
  AliAODMCHeader *mch = NULL;
  - AliAODEvent * aod = dynamic_cast<AliAODEvent*> (fInputEvent);
  + AliAODEvent * aod = NULL;
  +
  + if ( fEmbeddedEvent[0] && !fEmbeddedEvent[1] )
  + aod = dynamic_cast<AliAODEvent*> (AliAnalysisTaskEmcalEmbeddingHelper::GetInstance()->GetExternalEvent());
  + else
  + aod = dynamic_cast<AliAODEvent*> (fInputEvent);
  +
  if(aod) mch = dynamic_cast<AliAODMCHeader*>(aod->FindListObject("mcHeader"));
  return mch;
  