[BUG]: "Shrink database file" arbitrary selects itself upon database cleanup

[sakkamade]

Derivation of #423 question.

Brief description of the issue.

The "Shrink database file" option being arbitrary selected after database cleanup.

How to reproduce the bug?

1. Tools -> Cleanup database
2. Select some deletion criteria and uncheck "Shrink database file"
3. Click "OK"
4. Observe appearing of the check mark beside the "Shrink database file" option

What will be the expected result?

It will not select itself voluntarily.

What actually happens?

It selects itself.

Other information

Also, some side notes:

1. In my opinion, after completion of cleanup, some pop-up box like "The cleanup is completed" should be displayed.
   Otherwise, at the least, "Database cleanup is completed" should be in big, bold font with some mark at the left side of it.
   For instance, "⚠ Database cleanup is completed."
2. To "Shrink database file" option must be appended the information of its actual necessity, for example "to remove empty sectors in database file", either in parenthesis (preferable) or as tooltip.
   Otherwise the parenthesis should contain but word "recommended", while tooltip will present an explanation.

• OS: Arch Linux, KDE
• RSS Guard
  Version: 4.0.0 (built on Linux/x86_64)
  Revision: 98e850e
  Build date: 06/06/2021 02:40
  Qt: 5.15.2 (compiled against 5.15.2)