Fixed subrequest status not checked.

Closes #3219106

src/EntityToJsonApi.php

@@ -112,6 +112,21 @@ class EntityToJsonApi {
       $request->setSession($this->session);
     }
     $response = $this->httpKernel->handle($request, HttpKernelInterface::SUB_REQUEST);
+
+    if (!$response->isOk()) {
+      $json = $response->getContent();
+      $data = Json::decode($json);
+
+      throw new \Exception(sprintf(
+        "Error making subrequest to JSON:API to get '%s' entity with ID '%s' of bundle '%s'. Status code %s with message '%s'.",
+        $entity->getEntityTypeId(),
+        $entity->id(),
+        $entity->bundle(),
+        $response->getStatusCode(),
+        $data['errors'][0]['detail'] ?? ''
+      ));
+    }
+
     return $response->getContent();
   }