Add protection for duplicate index when cloning MCVertex

As discussed in LHCBGAUSS-1065 - See https://its.cern.ch/jira/browse/LHCBGAUSS-1065?focusedCommentId=1663175&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1663175

MicroDST/MicroDSTTools/src/MCVertexCloner.cpp

-// $Id: MCVertexCloner.cpp,v 1.6 2010-08-11 12:52:52 jpalac Exp $
 // Include files
 
 // from Gaudi
@@ -81,15 +80,15 @@ MCVertexCloner::cloneDecayProducts(const SmartRefVector<LHCb::MCParticle>& produ
     if ( productClone )
     {
       productClone->setOriginVertex( clonedVertex );
-      clonedVertex->addToProducts( productClone );
+      const bool found = std::any_of( clonedVertex->products().begin(),
+                                      clonedVertex->products().end(),
+                                      [&productClone]( const SmartRef<LHCb::MCParticle> mcP )
+                                      { return mcP.target() == productClone; } );
+      if ( !found ) { clonedVertex->addToProducts( productClone ); }
     }
   }
 }
 
-//=============================================================================
-// Destructor
-//=============================================================================
-MCVertexCloner::~MCVertexCloner() {}
 
 //=============================================================================