Added file existence assertion before CMDOWS parsing.

Former-commit-id: cdb93017cef3664f59486ea8e67f2ba64ae988b8

kadmos/cmdows/cmdows.py

@@ -37,6 +37,7 @@ class CMDOWS(object):
         self.XMLNS_PREFIX = 'https://bitbucket.org/imcovangent/cmdows/raw/master/schema/'
         self.XMLNS_SUFFIX = '/cmdows.xsd'
         if file_path:
+            assert os.path.isfile(file_path), 'File {} does not seem to exist.'.format(file_path)
             self.file = file_path
         if element is not None:
             self.root = ElementTree(element).getroot()