message: Let check_pydot return False if Graphviz is not installed
diff: @@ -49,7 +49,7 @@ def check_pydot():
  # to check the pydot/graphviz installation.
  pydot.Dot.create(pydot.Dot())
  return True
  - except OSError:
  + except (OSError, pydot.InvocationException):
  return False
  