Comment 5 for bug 952372

It seems, there are cases where this code

  for (tl= parent_lex->leaf_tables.head(); tl->next_local; tl= tl->next_local)
  {}
  tl->next_local= jtbm;

in convert_subq_to_jtbm() does the wrong thing. I am not currently sure what that should be replaced with.