[TDF] members of leaflists (e.g. "b.v") are not recognized as valid column names

#include <ROOT/TDataFrame.hxx>

#include <TBrowser.h>

#include <TCanvas.h>

#include <TTree.h>

#include <iostream>

#include <random>

using namespace std;

struct BrVal {

    Float_t a;

    Int_t i;

};

int main() {

    auto t = new TTree("t", "t");

    BrVal val;

    t->Branch("b", &val, "a/F:i/I");

    mt19937 rng;

    normal_distribution<Float_t> nd1(0, 1);

    uniform_int_distribution<Int_t> ud(-10, 10);

    for (size_t n = 1000; n; --n) {

        val.a = nd1(rng);

        val.i = ud(rng);

        t->Fill();

    }

    using TDF = ROOT::Experimental::TDataFrame;

    try {

        TDF df(*t);

        df.Histo1D("b.a")->Draw();

        auto h = df.Define("aa", [](Float_t bv) { return bv; }, {"b.a"}).Histo1D("aa");

        h->GetEntries();

    } catch (std::runtime_error &e) {

        cout << e.what() << '\n';

    }

    return 0;

}