[tmva] branches on stack, local scope, reset before return

Fixes root-project#10010

All the credit for this fix goes to pcanal and anaumann

tmva/tmva/src/DataSet.cxx

@@ -820,6 +820,7 @@ TTree* TMVA::DataSet::GetTree( Types::ETreeType type )
       delete[] metVals[i];
    delete[] metVals;
 
+   tree->ResetBranchAddresses();
    return tree;
 }