Adds defensive coding to make sure warnings don't happen.

[thijsoo]

Context

• We want to add some defensive coding so that we don't throw warnings when our code runs.

Summary

This PR can be summarized in the following changelog entry:

• Adds defensive coding to the suppress warnings on archive pages with the /%category%/%postname%/ permalink structure. Props to @Mte90.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Install and enable Elementor.
• Make sure Landing pages are enabled here: /wp-admin/admin.php?page=elementor#tab-experiments
• Set your permalink structure to a custom structure with /%category%/%postname%/
• Create a new landing page in elementor (it is an option in the templates CPT from elementor)
• Without this PR make sure you get 5 warnings when visiting the front-end of the landing page.
• With the PR make sure they are gone.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Block/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[Mte90]

I have those issue without Elementor, just to document better :-)

[igorschoester]

CR && AC ✅