[Forwardport] Fix the issue with "Shipping address is not set" exception

[dmytro-ch]

Original PR: #16753

The exception is being thrown instead of redirecting the customer to New Shipping Address form.

Description

The issue appeared because of the interrupted shipment assignment process.
As result, the incorrectly assigned record appears in quote_address table, which causes the additional error on Shopping Cart page, after performing the steps mentioned in Manual testing scenarios.
The issue has been fixed by replacing the StateException throw with void return statement in
\Magento\Quote\Model\ShippingMethodManagement::apply method. This method is being called by \Magento\Quote\Model\Quote\ShippingAssignment\ShippingProcessor::save.

Fixed Issues

1. "Shipping address is not set" exception in Multishipping Checkout. #16555: "Shipping address is not set" exception in Multishipping Checkout.

Manual testing scenarios

1. Log In as Customer.
2. Add Product to Cart.
3. Proceed to Checkout.
4. Fill Shipping Address data, click Next (do not place Order)
5. Return to the Storefront.
6. Go to the Shopping Cart.
7. Click Check Out with Multiple Addresses.

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 @dmytro-ch. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[rogyar]

Original PR is merged. Please, adjust the port to include all changes from the original PR. Thank you.

[dmytro-ch]

@rogyar I've updated the PR. Thank you!

[magento-engcom-team]

Hi @dmytro-ch. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.