fix: notifier state get's never persisted in database

- ever time the notification starts, it reports a corrupted state
  because the state never gets stored in the databse.
  saving the state in the database using `UPDATE` sql only works
  when there is already one entry in the table, otherwise the query
  will run through with zero updated rows.
  so in the case when the state cannot be loaded, we properly create
  one record inside the notifier_state table

src/oncall/notifier/reminder.py

@@ -48,8 +48,12 @@ def reminder(config):
     cursor.execute('SELECT `last_window_end` FROM `notifier_state`')
     if cursor.rowcount != 1:
         window_start = int(time.time() - interval)
-        logger.warning('Corrupted/missing notifier state; unable to determine last window. Guessing %s',
+        logger.warning('Corrupted/missing notifier state; unable to determine last window. Guessing %s. Creating state in database',
                        window_start)
+        # create a clean state in the datebase
+        cursor.execute('DELETE FROM `notifier_state`')
+        cursor.execute('INSERT INTO `notifier_state` (`last_window_end`) VALUES (%s) ', window_start)
+        connection.commit()
     else:
         window_start = cursor.fetchone()[0]