ImageServiceImpl: reduce duplication between add() and replace()

[0pdd]

The puzzle 1303-7320596f from #1303 has to be resolved:

mystamps/src/main/java/ru/mystamps/web/feature/image/ImageServiceImpl.java

Line 84 in 4c2104a

// @todo #1303 ImageServiceImpl: reduce duplication between add() and replace()

The puzzle was created by Slava Semushin on 28-Apr-20.