sanity checking after calling a filter

Maybe addresses https://github.com/GigaOM/legacy-pro/issues/2085
better sanity checking

Fixes the following error:

[Thu Jan 09 18:55:46 2014] [error] [client 65.55.213.239] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')\n\t\t\t\tGROUP BY c.term_taxonomy_id ORDER BY count DESC LIMIT 2000' at line 5 for query SELECT b.term_id, c.term_taxonomy_id, b.slug, b.name, a.taxonomy, a.description, COUNT(c.term_taxonomy_id) AS `count`\n\t\t\t\tFROM wp_14_term_relationships c\n\t\t\t\tINNER JOIN wp_14_term_taxonomy a ON a.term_taxonomy_id = c.term_taxonomy_id\n\t\t\t\tINNER JOIN wp_14_terms b ON a.term_id = b.term_id\n\t\t\t\tWHERE c.object_id IN ()\n\t\t\t\tGROUP BY c.term_taxonomy_id ORDER BY count DESC LIMIT 2000 made by require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), include('/themes/nhrsa-oulipo/index.php'), get_sidebar, locate_template, load_template, require_once('/themes/nhrsa-oulipo/sidebar.php'), dynamic_sidebar, call_user_func_array, WP_Widget->display_callback, Scrib_Facets_Widget->widget, Facet_Taxonomy->get_terms_in_found_set
later code expects an array
warnings cleanup

See https://github.com/GigaOM/legacy-pro/issues/2092
Merge pull request #35 from misterbisson/bug-fixes

Trying to catch an error, better sanity checking all around