[Forwardport] Fix zero price simple failed to resolve as default

[mage2pratik]

Original Pull Request

#16540

Description

When two simple products of a configurable have different prices, the lowest price simple product is expected to resolve as the default price showing on product detail page.

If one of the simple products has price=0, it will fail to resolve as default.

Notice that it is an edge case having price=0 product. It probably is still worth fixing.

Fixed Issues (if relevant)

Can't find any related issues at the moment

Manual testing scenarios

1. Set up a configurable with two simple products. One simple have price at £3, another at £0
2. The simple products with LOWER product id must be at £0
3. Go to product detail page of the configurable

Expected result: Default price rendered as £0
Actual result: Default price rendered as £3

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

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[magento-engcom-team]

Hi @mage2pratik. 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.