[IO] TTreeReader: Add test for disappearing column in TChain
[IO] TTreeReader: Add test for disappearing column in TChain

root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,olifre/root,root-mirror/root,karies/root,olifre/root,karies/root,olifre/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,karies/root,olifre/root