Prevent fatal error when filtered block categories array is null.

[kmgalanakis]

Description of the Change

This PR adds a fix to prevent a PHP fatal error when the value of the filtered block categories is not an array. This could happen when a third-party plugin or them is modifying the value of the filtered block categories with a non-appropriate value.

Closes #199

How to test the Change

Add the following to your theme's function.php file

add_action( 'block_categories_all', 'nullify_block_categories' );
function nullify_block_categories() {
    return null;
}

Changelog Entry

Fixed - Prevent PHP fatal error when the value of the filtered block categories is not an array.

Credits

Props @kmgalanakis

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests pass.