fix bug with not allowed_content part for properties

backend/tracim_backend/models/data.py

@@ -1181,8 +1181,8 @@ class Content(DeclarativeBase):
         else:
             properties = json.loads(self._properties)
         if CONTENT_TYPES.get_one_by_slug(self.type) != CONTENT_TYPES.Event:
-            if self._properties and not 'allowed_content' in self._properties:
-                properties['allowed_content'] = CONTENT_TYPES.default_allowed_content_properties(self.type)
+            if not 'allowed_content' in properties:
+                properties['allowed_content'] = CONTENT_TYPES.default_allowed_content_properties(self.type)  # nopep8
         return properties
 
     @properties.setter