Fix/wrong cf on write to vault

[felsweg-iota]

Description of change

This PR corrects a wrong control flow in client/src/write_to_vault, that always returned an error even if the operation was successful.

Links to any relevant issues

none.

Type of change

Choose a type of change, and delete any options that are not relevant.

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

How the change has been tested

client/src/tests/interface_tests.rs have been extended to detect this kind of behavior.

Change checklist

Add an x to the boxes that are relevant to your changes, and delete any items that are not.

• 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
• New and existing unit tests pass locally with my changes

[elenaf9]

Looks good to me. Just a minor nitpick on the result matching, to avoid the unwrap.

[elenaf9]

Suggested change

	if result.is_ok() {
	return StatusMessage::OK;
	} else {
	return StatusMessage::Error(result.err().unwrap().to_string());
	}
	return match result {
	Ok(_) => StatusMessage::OK,
	Err(e) => StatusMessage::Error(e.to_string()),
	};