[16.0][FIX] product_variant_configurator: change instance checking

[Mantux11]

Creating a new Sales Order and selecting a product in the SO line, and choosing any subscription period results in a technical error.

Checking instance (_name) should not be on a specific record, it could be done on all products. And if there is no products, getting to first record raises and Index out of range error.

This fixes Index out of range error.

[github-actions[bot]]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days. If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.

[Du-ma]

@carolinafernandez-tecnativa Mind having a look since you migrated this to 16.0 and all.

[OCA-git-bot]

Hey, thanks for contributing! Proceeding to merge this for you. Prepared branch 16.0-ocabot-merge-pr-346-by-pedrobaeza-bump-patch, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at 1f598ec7f683a4bb0e69cb199e733c469df0093c. Thanks a lot for contributing to OCA. ❤️