Update series: add validation for a price

[0pdd]

The puzzle 1340-34ef47fe from #1340 has to be resolved:

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

Line 53 in 49498ab

// @todo #1340 Update series: add validation for a price

The puzzle was created by Slava Semushin on 05-Jun-20.