[CBR-400] Fix wallet failing to start

[ruhatch]

Description

CDEC-509 introduced a bug that stopped the wallet from starting. This fixes it by using Maybe GeneratedSecrets where necessary.

Linked issue

CBR-400

Type of change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• [~] 🛠 New feature (non-breaking change which adds functionality)
• [~] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)
• [~] 🏭 Refactoring that does not change existing functionality but does improve things like code readability, structure etc
• [~] 🔨 New or improved tests for existing code
• [~] ⛑ git-flow chore (backport, hotfix, etc)

Developer checklist

• I have read the style guide document, and my code follows the code style of this project.
• If my code deals with exceptions, it follows the guidelines.
• I have updated any documentation accordingly, if needed. Documentation changes can be reflected in opening a PR on cardanodocs.com, amending the inline Haddock comments, any relevant README file or one of the document listed in the docs directory.
• [~] CHANGELOG entry has been added and is linked to the correct PR on GitHub.

Testing checklist

• [~] I have added tests to cover my changes.
• All new and existing tests passed.

QA Steps

Screenshots (if available)

[robahub]

I want to add my review?

[erikd]

Looks good and can confirm that this has fixed it.

[erikd]

Going to merge this.