Fix unwanted unshielding notice after recovery

[Radiokot]

Purpose

Fix unwanted unshielding notice after recovery – when no accounts ever had shielded balance.

Changes

• Do not store empty shielded balances as ENCRYPTED on recovery.

Checklist

• [x] My code follows the style of this project.
• [x] The code compiles without warnings.
• [x] I have performed a self-review of the changes.
• [x] I have documented my code, in particular the intent of the hard-to-understand areas.
• [ ] (If necessary) I have updated the CHANGELOG.