fix: only show category link anchor tags if the category has a link

[dkoo]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go 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:

Homepage Posts and Post Carousel front-end templates render category terms with a link. This omits the a anchor tag in the unlikely event that a term lacks a link. This could happen if the term being rendered is a "pseudo term", or a term that's appended programmatically to a post's term output based on some condition other than a true taxonomy term applied to the post.

The use case this comes from: a "featured" post meta toggle which programmatically shows a "featured" category label alongside the post's other categories. In this case the "featured" category label is not tied to a true category term, therefore it has no term link.

Bonus: also ensures that if a post with no categories (not even "Uncategorized") gets rendered by Homepage Posts or Post Carousel with categories enabled, the editor renders nothing instead of 0.

How to test the changes in this Pull Request:

1. Set up code to add a "pseudo term" to a post. In your theme's functions.php, temporarily add the following filter:

function newspack_add_pseudo_label( $categories ) {
	$pseudo_term = new \WP_Term(
		(object) [
			'name'     => 'Pseudo Category',
			'slug'     => 'my-fake-category',
			'taxonomy' => 'category',
		]
	);

	// Add pseudo label in front of true categories.
	array_unshift( $categories, $pseudo_term );

	return $categories;
}
add_filter( 'get_the_categories', 'newspack_add_pseudo_label' );

2. Add Homepage Posts and Post Carousel blocks to a post. Ensure that both blocks render some posts.
3. On master, observe on the front-end that the "Pseudo Category" labels get rendered with empty anchor tags (<a href="">Pseudo Category</a>).
4. Check out this branch, refresh, observe that the "Pseudo Category" labels are rendered as styled plain text without links.

Test no categories

1. Modify your filter above to render no categories, not even the default category:

function newspack_add_pseudo_label( $categories ) {
	return [];
}
add_filter( 'get_the_categories', 'newspack_add_pseudo_label' );

2. Add Homepage Posts and Post Carousel blocks to a post. Ensure that both blocks render some posts and that "Show Categories" is turned on.
3. On master, observe that items in the editor show 0 in place of categories:

4. Check out this branch, refresh the editor, confirm that nothing is shown instead of 0.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[miguelpeixe]

Working as described! 💯

[matticbot]

🎉 This PR is included in version 1.37.0-alpha.2 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.37.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀