Correct default params for LimitIterator constructor

src/UNL/Catalog/CourseSearch/DBSearcher.php

@@ -2,7 +2,7 @@
 class UNL_Catalog_CourseSearch_DBSearcher extends UNL_UndergraduateBulletin_CourseSearch_DBSearcher
 {
 
-    function getQueryResult($query, $offset = 0, $limit = null)
+    function getQueryResult($query, $offset = 0, $limit = -1)
     {
         $query =  'SELECT DISTINCT courses.id, courses.xml FROM courses INNER JOIN crosslistings ON courses.id=crosslistings.course_id WHERE crosslistings.courseNumber >= "500" AND (' . $query . ');';
         return new UNL_UndergraduateBulletin_CourseSearch_DBSearchResults($query, $offset, $limit);