[Admin] Can not change donation to membership if no linked adherent

src/Admin/DonationAdmin.php

@@ -138,7 +138,7 @@ protected function configureFormFields(FormMapper $form): void
                 ->add('membership', CheckboxType::class, [
                     'label' => 'Cotisation',
                     'required' => false,
-                    'disabled' => $donation->isMembership(),
+                    'disabled' => $donation->isMembership() || null === $donation->getDonator()?->getAdherent(),
                 ])
                 ->add('code', null, [
                     'label' => 'Code don',