[Forwardport] 'Allowed Countries' - get countries for scope 'default'.

[mage2pratik]

Original Pull Request

#16693

Description

• fix 'if' for scope with id 0;
• add test for this case;

Fixed Issues

1. magento/magento2#?: Not found relevant issue for the problem

Manual testing scenarios

Pre-conditions

1. Installation with website - Website and tore - Store.
2. Configured different 'Allowed Countries' for 'Default' and Store scopes.

Steps To Reproduce

1. Require Magento\Directory\Model\AllowedCountries class
2. Get Allowed Countries for default scope 0:
   Magento\Directory\Model\ResourceModel\Country::getAllowedCountries('ScopeInterface::SCOPE_STORE, 0)

Expected Result:

1. Returned Allowed Countries for Default config

Actual Result:

1. Will be returned Allowed Countries for default store - Store.

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 @mage2pratik. 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

[swnsma]

FP for PR #16693 already created: #16694