When the user comes from outside the site, the destination of the "Go Back" button will be an external site.

Problem/Motivation

In the description for the "Custom URL" on the module page, it says:
This url will be used also if the user comes from outside the site and the smart mode is activated.

However, when the user comes from outside the site, the destination of the "Go Back" button will be an external site.

Could this be a bug?

Steps to reproduce

1. Install Drupal core 10.5.0 and the go_back module version 8.x-1.8.
2. Open the Block layout administration page (/admin/structure/block) and place the Go Back Block in any desired region. Configure it as follows:
- Check "Active button in Article". (Other entity types are also acceptable.)
- Check "Active smart mode in Article".
- In "URL Back - Article", enter any URL, for example `/node`.
3. On an external (non-Drupal) page, embed a link to a Drupal page that displays the Go Back Block, and click the link.
4. Click the "Go Back" button.