fix: Handle errors on placeOrder mutations

The PlaceOrder resolver does not necessary return an order, in case of errors. See https://github.com/magento/magento2/blob/2.4-develop/app/code/Magento/QuoteGraphQl/Model/Resolver/PlaceOrder.php#L106

Plugin/GraphQlPlaceOrderAddCartId.php

@@ -59,6 +59,10 @@ public function __construct(
      */
     public function afterResolve(PlaceOrder $placeOrder, array $result): array
     {
+        if (!isset($result['order'])) {
+            return $result;
+        }
+
         try {
             $cart = $this->quoteHelper->getQuoteByOrderIncrementId($result['order']['order_number']);
             $maskedId = $this->quoteIdToMaskedQuoteId->execute($cart->getId());