Fix "PHP Warning: implode(): Invalid arguments passed in search-weights.php:17"

[Krinkle]

The Apache2 error logs (via splunk.jquery.com) are full of these:

 PHP Warning:  implode(): Invalid arguments passed in /var/www/wordpress/jquery-wp-content/mu-plugins/api-sites/search-weights.php on line 17
PHP message: PHP Warning:  Invalid argument supplied for foreach() in /var/www/wordpress/jquery-wp-content/mu-plugins/api-sites/search-weights.php on line 24
PHP message: PHP Warning:  implode(): Invalid arguments passed in /var/www/wordpress/jquery-wp-content/mu-plugins/api-sites/search-weights.php on line 17
PHP message: PHP Warning:  Invalid argument supplied for foreach() in /var/www/wordpress/jquery-wp-content/mu-plugins/api-sites/search-weights.php on line 24
..

Possibly caused by 2aaf08d.

[scottgonzalez]

This started with the WordPress 4.0 update.