[TDF] Use a meaningful name for the commented out function parameter

Author: bluehood

tree/treeplayer/inc/ROOT/TDFInterface.hxx

@@ -1092,7 +1092,7 @@ protected:
 
          bool FirstEvent = true;
          // TODO move fillTree and initLambda to SnapshotHelper's body
-         auto fillTree = [&t, &bnames, &FirstEvent](unsigned int /* unused */, Args &... args) {
+         auto fillTree = [&t, &bnames, &FirstEvent](unsigned int /* slot */, Args &... args) {
             if (FirstEvent) {
                // hack to call TTree::Branch on all variadic template arguments
                std::initializer_list<int> expander = {(t.Branch(bnames[S].c_str(), &args), 0)..., 0};