Save checklist even if no items are selected

[mjaakko]

Short description

Currently checklists are not saved to database if no items are selected. This can be a problem for example if the final review checklist contains only minimum requirements and none of them are selected.

DoD

I have:

• [x] added actual code.
• [x] produced clean code that passes ESLint.
• [x] code that actually does what it should.
• [ ] documented the code or added documentation to the wiki.
• [ ] added or modified test(s).
• [x] test(s) that actually pass.
• [x] works in trunk branch