Update series: handle refuse to update an existing comment gracefully

[0pdd]

The puzzle 785-c33d2a08 from #785 has to be resolved:

mystamps/src/main/java/ru/mystamps/web/feature/series/JdbcSeriesDao.java

Line 150 in 7be4e62

// @todo #785 Update series: handle refuse to update an existing comment gracefully

The puzzle was created by Slava Semushin on 24-May-20.