Ensure echoing when escaping attributes

[mircobabini]

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• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Resolves the issue we had about required field not filled in in checkout without additional warning.
This is because when not using international addresses, the default country is not written into the hidden field.

How to test the changes in this Pull Request:

1. Deactivate international addresses (via filter)
2. Then see the checkout working again

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully run tests with your changes locally?