[extensionDatabase] use latin-1 as json decoder

vispa/models/extension.py

@@ -34,7 +34,7 @@ class ExtensionDatabase(Base):
         if not isinstance(extension_database, ExtensionDatabase):
             return None
         data = extension_database.data
-        return data if not decode_json else json.loads(data)
+        return data if not decode_json else json.loads(data, encoding="latin-1")
 
     @staticmethod
     def update_data(db, extension_name, data, extension_database=None):