Check that the sample HDF5 file exists before opening it.
Check that the sample HDF5 file exists before opening it.

Change-Id: I37069d4c72d4f648cd8e65fbfd23516b6e8c7eb3

ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,cjh1/mongochemweb-avogadrolibs,ghutchis/avogadrolibs,ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,wadejong/avogadrolibs,ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,OpenChemistry/avogadrolibs,OpenChemistry/avogadrolibs,wadejong/avogadrolibs,cjh1/mongochemweb-avogadrolibs,wadejong/avogadrolibs,ghutchis/avogadrolibs,wadejong/avogadrolibs,cjh1/mongochemweb-avogadrolibs,cjh1/mongochemweb-avogadrolibs