Added checks to see if the payment is available

[michielgerritsen]

Fix an error while submitting an order without payment method.

Description

When submitting an order using the rest api without an payment, you would get an exception/error report due to the fact there was not payment method.

Fixed Issues (if relevant)

1. REST API create order POST /V1/orders #15652: REST API create order POST /V1/orders

Manual testing scenarios

1. Send an POST request to the rest/V1/orders endpoint containing the following:
   { "entity": { "base_grand_total" : 100, "customer_email" : "user@domain.tld", "grand_total" : 100, "items" : [ { "sku" : "TESTSEB" } ] } }

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-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

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

[magento-engcom-team]

Hi @michielgerritsen. 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.