[TreeProcMT] Trees in subdirectories are not supported (and their usage lead to a crash)

#include <TFile.h>

#include <TROOT.h>

#include <TTree.h>

#include <ROOT/TTreeProcessorMT.hxx>

void make_file()

{

   TFile f("test.root", "RECREATE");

   f.mkdir("dir");

   f.cd("dir");

   float x;

   TTree t("tree", "tree");

   t.Branch("x", &x, "x");

   for (auto i = 0; i < 10; i++) {

      x = (float)i;

      t.Fill();

   }

   t.Write();

   f.Write();

   f.Close();

}

void test()

{

   make_file();

   ROOT::EnableThreadSafety();

   TFile f("test.root");

   auto t = (TTree *)f.Get("dir/tree");

   ROOT::TTreeProcessorMT tp(*t);

   tp.Process([](TTreeReader &r) { while (r.Next()); });

}

int main()

{

   test();

   return 0;

}

#8  0x00007fc730401c7e in ROOT::Internal::MakeClusters (treeName="tree", fileNames=std::vector of length 1, capacity 1 = {...}) at /home/eguiraud/ROOT/root/tree/treeplayer/src/TTreeProcessorMT.cxx:51

#9  0x00007fc7304036ba in ROOT::TTreeProcessorMT::<lambda(std::size_t)>::operator()(std::size_t) const (__closure=0x7ffebb4c5a30, fileIdx=0) at /home/eguiraud/ROOT/root/tree/treeplayer/src/TTreeProcessorMT.cxx:280

#10 0x00007fc730403d3a in ROOT::TThreadExecutor::<lambda(unsigned int)>::operator()(unsigned int) const (__closure=0x7ffebb4c59d0, i=0) at /home/eguiraud/ROOT/dbg/include/ROOT/TThreadExecutor.hxx:145

#11 0x00007fc7304040fc in std::_Function_handler<void(unsigned int), ROOT::TThreadExecutor::Foreach(F, std::vector<T, std::allocator<_T2> >&) [with F = ROOT::TTreeProcessorMT::Process(std::function<void(TTreeReader&)>)::<lambda(std::size_t)>; T = long unsigned int]::<lambda(unsigned int)> >::_M_invoke(const std::_Any_data &, unsigned int &&) (__functor=..., __args#0=