do not allow empty XML directory

src/rougail/xmlreflector.py

@@ -65,6 +65,8 @@ class XMLReflector:
             filenames = [join(xmlfolder, filename) for filename in listdir(xmlfolder) if \
                          filename.endswith('.xml')]
             filenames.sort()
+            if not filenames:
+                raise DictConsistencyError(_('there is no XML file'), 77, [xmlfolder])
             for xmlfile in filenames:
                 try:
                     document = parse(xmlfile)