Issue #3480202: Exception when membership is deleted after user

Closes #3480202

ginvite.module

@@ -206,8 +206,8 @@ function ginvite_group_relationship_delete(GroupRelationshipInterface $group_rel
   // Remove invitation when member is removed.
   if ($plugin_id == 'group_membership') {
     $properties = [
-      'entity_id' => $group_relationship->getEntity()->id(),
-      'gid' => $group_relationship->getGroup()->id(),
+      'entity_id' => $group_relationship->getEntityId(),
+      'gid' => $group_relationship->getGroupId(),
     ];
 
     // Remove invitations, when we remove the user.