[bug] Duplicate Hardcover API Keys cause an internal server error.

[Zurtar]

Describe the bug
Duplicate Hardcover API Keys cause an internal server error.

To Reproduce
Steps to reproduce the behavior:

1. Set the HardCover API Key for some user as FOO
2. Set the HardCover API Key for some other user as FOO
3. Save/Apply
4. See error message
5. Click Return To Home
6. See Error

Expected behavior
The error is expected as the column has a unique constraint. But the error should be handled gracefully and the return to home button should still work normally, rolling back the users attempted config change.

Configuration(please complete the following information):

• OS: Debian (6.12.69+deb13-amd64)
• Hardware: Proxmox VM
• Version: v4.0.6