Log complete error message on BadResponseExceptions, not truncated Guzzle message.

Closes #3489264

src/Controller/CheckoutController.php

@@ -129,7 +129,13 @@ class CheckoutController extends ControllerBase {
       return new JsonResponse(['id' => $paypal_order['id']]);
     }
     catch (BadResponseException $exception) {
-      $this->logger->error($exception->getResponse()->getBody()->getContents());
+      // Log untrimmed exception:
+      if ($exception->hasResponse()) {
+        $this->logger->error($exception->getResponse()->getBody()->getContents());
+      }
+      else {
+        $this->logger->error($exception->getMessage());
+      }
       $message = $this->t('Payment failed. Please review your information and try again.');
       return new JsonResponse(['message' => $message], Response::HTTP_BAD_REQUEST);
     }