AddSimilarSeriesForm: add integration test that similarSeriesIds isn't empty

[0pdd]

The puzzle 1448-d5a68b83 from #1448 has to be resolved:

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

Line 59 in 2f40baa

// @todo #1448 AddSimilarSeriesForm: add integration test that similarSeriesIds isn't empty

The puzzle was created by Slava Semushin on 21-Jun-20.