Changes from '=' to 'LIKE'

Should fix issues with Oracle DB / CLOB

classes/framework.php

@@ -1123,7 +1123,7 @@ class framework implements \H5PFrameworkInterface {
         return (int) $DB->get_field_sql(
                 "SELECT COUNT(id)
                    FROM {hvp}
-                  WHERE filtered = ''");
+                  WHERE filtered LIKE ''");
     }
 
     /**