Link error "The internal path component is invalid"

Steps to reproduce

1. create an entity type that includes AJAX calls on the node edit form, e.g. node with a link field and a media field, or a field with multiple elements and "add another" links
2. as a user without the 'link to any page' permission, try to create an instance of that entity
3. enter an invalid path in the link field, e.g. 'foo'
4. click on the button that initiates an AJAX request, e.g. file upload, add another

Expected result

An error message should appear about the invalid internal path, but you should be able to proceed with the action

Actual result

It isn't possible to proceed.
The AJAX call responds with a 500 error "The internal path component is invalid. Its path component must have a leading slash" with field widget type "Link".

↵An AJAX HTTP error occurred.↵HTTP Result Code: 500↵Debugging information follows.↵Path: /fr/node/6/edit?element_parents=field_test/widget/0&destination=/admin/content&ajax_form=1↵StatusText: 500 Service unavailable (with message)↵ResponseText: The website encountered an unexpected error. Please try again later.InvalidArgumentException: The internal path component 'test' is invalid. Its path component must have a leading slash, e.g. internal:/foo.

This error generates from \Drupal\Core\Url::fromInternalUri

It happens from \Drupal\link\Plugin\Field\FieldWidget\LinkWidget::formElement
in code
$item->getUrl()->access() (core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php:175)

For avoidance of this error we have next element validator where check input values
\Drupal\link\Plugin\Field\FieldWidget\LinkWidget::validateUriElement

So we can't catch this error on common entity save operation.
But we can catch it with any additional ajax buttons, which skip validation with #limit_validation_errors

It appears on all browsers.

In my example "foo" value is incorrect for Link field. We can avoid this error by putting only correct values. But customer can be confused. He doesn't know what values are correct, and he doesn't know why all his AJAX buttons don't work. So we should avoid 500 error with ajax buttons.

I have investigated this issue and found, that we need to add additional check in \Drupal\link\Plugin\Field\FieldWidget\LinkWidget::formElement
I have prepared patch and I will apply it in comment.