Simple entity merge: check for content entity

check-for-content-entity.patch

diff --git a/simple_entity_merge.module b/simple_entity_merge.module
index 277824e..1dae9fb 100644
--- a/simple_entity_merge.module
+++ b/simple_entity_merge.module
@@ -12,6 +12,9 @@ use Drupal\Core\Entity\EntityInterface;
  */
 function simple_entity_merge_entity_type_alter(array &$entity_types) {
   foreach ($entity_types as $entity_type_id => $entity_type) {
+    if (!$entity_type->isTranslatable()) {
+      continue;
+    }
     if (($entity_type->getFormClass('default') || $entity_type->getFormClass('edit')) && $entity_type->hasLinkTemplate('edit-form')) {
       $entity_type->setLinkTemplate('simple_entity_merge-execute', "/simple_entity_merge/$entity_type_id/{{$entity_type_id}}");
       $entity_type->setFormClass('simple_entity_merge', 'Drupal\simple_entity_merge\Form\Merge');