File usage is not handleded

Currently, the file usage of Drupal is not handled. When you save the logo for the domain, after that you receive the following error:

Error message
The file used in the Upload logo for Domain: test.org field may not be referenced.

Issue is solved in my patch.

Bonus issue solved:
When you have more than one domain record and for one of them you don't set logo. On form submit the following error occurs;

Notice: Undefined offset: 0 in Drupal\domain_access_logo\Form\DomainAccessLogoSettingsForm->submitForm() (line 128 of modules/contrib/domain_access_logo/src/Form/DomainAccessLogoSettingsForm.php).

Both are solved.