Inconsistent types between DefineVariable<T> and InquireVariable<T>

Created by: germasch

To reproduce (on latest master):

#include <adios2.h>

void test1()
{
  using T = char;

  adios2::ADIOS ad(MPI_COMM_WORLD, adios2::DebugON);

  {
    adios2::IO io_writer = ad.DeclareIO("writer");
    auto var = io_writer.DefineVariable<T>("var");
    auto writer = io_writer.Open("test.bp", adios2::Mode::Write);
    
    T test = 99;
    writer.Put(var, test);
    writer.Close();
  }

  {
    adios2::IO io_reader = ad.DeclareIO("reader");
    auto reader = io_reader.Open("test.bp", adios2::Mode::Read);
    auto var = io_reader.InquireVariable<T>("var");
    assert(static_cast<bool>(var));
    
    T test;
    reader.Get(var, test);
    reader.Close();

    assert(test == 99);
  }
}

int main(int argc, char** argv)
{
  MPI_Init(&argc, &argv);
  test1(); 
  MPI_Finalize()
  return 0;
}

This test writes a single variable, and then tries to read it back again. The type of the variable can be changed with the using T = ... directive. The test succeeds with using T = int;, but using T = char; fails.

It also fails with using T = std::size:t and using T = unsigned long.