delete before adding new layer

NonLinearSolver/modelReduction/ANNUtils.cpp

@@ -220,6 +220,7 @@ void ArtificialNN::addLayer(int index, const DenseLayer& layer)
   else
   {
     // we add pointer to existing object instead of creating a new one
+    if (_allLayers[index] != NULL) delete _allLayers[index];
     _allLayers[index] = layer.clone();
     Msg::Info("add layer: %d",index);
     _allLayers[index]->print_infos();