1763: show flash messages again r=mergify[bot] a=lub
## What type of PR?
bug-fix
## What does this PR do?
This basically restores the behaviour, that got removed in
ecdf0c25b3 during refactoring.
### Related issue(s)
- noticed it while reviewing #1756
## Prerequistes
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.
- [-] In case of feature or enhancement: documentation updated accordingly
- [-] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.
Co-authored-by: lub <git@lubiland.de>
47d6c697d0