Prevent undefined property warnings during search.

[peterwilsoncc]

Description of the Change

To avoid modifying the search query clause twice, the redirect term is discarded after the WHERE clause is generated.

The use of unset() triggers warnings as the second call to the filter is attempting to access an undefined property. This changes the code to set the search term to false to prevent the second and subsequent runs of the filter.

Closes #399

How to test the Change

1. Enable all logging of errors in your wp-config.php file:

   define( 'WP_DEBUG', true );
   define( 'WP_DEBUG_DISPLAY', true );
   define( 'WP_DEBUG_LOG', true );

2. Configure the site to run on PHP 8.0+ (this is when the error level became a warning)
3. Create a redirect
4. Search redirects
5. Check the logs to ensure a warning is not recorded. On single site installs the log is located in the default wp-content folder.
   • on trunk a warning will be thrown
   • on this branch no warning will be thrown

Changelog Entry

Fixed - Prevent undefined property warnings when searching redirects.

Credits

Props @chermant, @Sidsector9, @peterwilsoncc

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[Sidsector9]

Thanks for fixing this @peterwilsoncc!