Preserve custom logout URL when OIDC logout is configured

[BytesUnlimited-net]

Summary

This change prevents Plugin.CustomAuth_custom_logout from being unintentionally removed when OIDC logout is enabled.

Fixes #409

Problem

configure.sh sets Plugin.CustomAuth_custom_logout when the required logout parameters are provided. However, later in the script the setting may be unset again when CUSTOM_AUTH_ENABLE is not enabled.

As a result, configurations that rely on OIDC logout can lose their custom logout URL even though it was configured correctly earlier in the script.

Solution

Only unset Plugin.CustomAuth_custom_logout when OIDC logout is not enabled or when no OIDC logout URL has been provided.

This prevents the OIDC-specific logout configuration from being overwritten by the generic cleanup logic.

Impact

• Preserves configured OIDC logout URLs.
• Prevents valid logout configuration from being removed later in the script.
• Makes the configuration logic consistent when OIDC is used without CUSTOM_AUTH_ENABLE.