Merge pull request #774 in VECTO/vecto-sim from...

Merge pull request #774 in VECTO/vecto-sim from ~EMQUARIMA/vecto-sim:bugfix/VECTO-1020-hashingtool-crashes to ReleaseCandidates/v3.3.3.1609

* commit '39b48529':
  surround loading files with try/catch, handle null validation argument
  xmlvalidator: in case the file to validate is not of a known schema, call the validation callback with null as arguments.
  hashing tool: adding expected document type in viewmodels