fix: add a couple guards for anonymous users

This fixes a couple places (LastSeenCoursewareTimezone and
UserCourseTag) where we were saving an entry for a user, but not
making sure we ignored anonymous users.

openedx/core/djangoapps/courseware_api/views.py

@@ -498,6 +498,9 @@ class CoursewareInformation(RetrieveAPIView):
         The timezone in the user's account is frequently not set.
         This method sets a user's recent timezone that can be used as a fallback
         """
+        if not user.id:
+            return
+
         cache_key = 'browser_timezone_{}'.format(str(user.id))
         browser_timezone = self.request.query_params.get('browser_timezone', None)
         cached_value = TieredCache.get_cached_response(cache_key)