Delete UNTIS lessons without lesson periods while importing

aleksis/apps/untis/util/mysql/importers/lessons.py

@@ -40,14 +40,14 @@ def import_lessons(
     for lesson in tqdm(lessons, desc="Import lessons", **TQDM_DEFAULTS):
         lesson_id = lesson.lesson_id
 
-        existing_lessons.append(lesson_id)
-
         logger.info(_("Import lesson {}").format(lesson_id))
 
         if not lesson.lesson_tt:
             logger.warning(_("  Skip because missing times").format(lesson_id))
             continue
 
+        existing_lessons.append(lesson_id)
+
         # Split data (,)
         raw_lesson_data = connect_untis_fields(lesson, "lessonelement", 10)
         raw_time_data = lesson.lesson_tt.split(",")