Fix restore_backup()

[Thoralf-M]

Description of change

Fix restore_backup() when no secret manager data is stored inside

Type of change

• Bug fix (a non-breaking change which fixes an issue)

How the change has been tested

Added test and cli wallet

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes