Missing file gives an hd5 error rather than stating that it does not exist

If a solver finds that there is a missing .fld file (for example for a boundary condition file) an error is given that says (when Nektar_USE_hdf is not activated):

Fatal : Level 0 assertion violation No such module: Hdf5 Available classes: Xml: XML-based output of field data.

Probably need to amend the FieldIO::CreateForFile routine to properly check the existence of the file using boost::filesystem before we try to read it.