(Much) easier approach

application/models/Gridmap_model.php

@@ -179,6 +179,9 @@ class Gridmap_model extends CI_Model {
 	    if ($sql != '') {
 		    $sql=' and (1=0 '.$sql.')';
 	    }
+	    if ($sql == '') {
+		    $sql=' and 1=0';
+	    }
 	    return $sql;
     }