Update shipment collection to unserialize packages attribute after load

[dnsv]

Description

The column packages in sales_shipment is in its resource model \Magento\Sales\Model\ResourceModel\Order\Shipment characterized as a serializable field. But packages doesn't get unserialized when shipments are loaded with a collection. This pull request fixes the issue by unserializing the field after the collection is loaded.

Manual testing scenarios

1. Create a shipment through the backend. packages is in my case set to [].
2. Load this shipment with a collection. The attribute packages is a string, but should be an array.

class Shipment
{
    /**
     * @var \Magento\Sales\Model\ResourceModel\Order\Shipment\CollectionFactory
     */
    protected $shipmentCollectionFactory;

    /**
     * @var \Magento\Sales\Api\ShipmentRepositoryInterface
     */
    protected $shipmentRepository;

    public function __construct(
        \Magento\Sales\Model\ResourceModel\Order\Shipment\CollectionFactory $shipmentCollectionFactory,
        \Magento\Sales\Api\ShipmentRepositoryInterface $shipmentRepository
    ) {
        $this->shipmentCollectionFactory = $shipmentCollectionFactory;
        $this->shipmentRepository = $shipmentRepository;
    }

    public function execute()
    {
        /** @var \Magento\Sales\Model\Order\Shipment $shipment */
        $shipment = $this->shipmentRepository->get(1);
        echo gettype($shipment->getPackages()) . "\n";

        /** @var \Magento\Sales\Model\ResourceModel\Order\Shipment\Collection $shipmentCollection */
        $shipmentCollection = $this->shipmentCollectionFactory->create();
        $shipment = $shipmentCollection->addAttributeToFilter('entity_id', 1)
            ->getFirstItem();

        echo gettype($shipment->getPackages());
    }
}

In this example the same shipment is loaded with 1.) the shipment repository and 2.) the shipment collection. The output is:

array
string

This consequently causes further problems if the shipment loaded with the shipment collection is being updated, because packages gets saved as "[]" (the quotation marks are now a part of the string). packages now can't get unserialized when it's loaded with any method. Also an error is shown if this shipment is opened in the backend because an array is expected but a string is given:

Exception #0 (Exception): Warning: Invalid argument supplied for foreach() in /path/to/magento2/app/code/Magento/Shipping/view/adminhtml/templates/order/packaging/packed.phtml on line 12

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @dnsv. Thank you for your contribution
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[magento-engcom-team]

@dnsv thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[magento-engcom-team]

Hi @dnsv. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.