Handled undefined children in the gflib.js Fun.show() function.

This shouldn't really happen, but if it does, debugging is much easier.

lib/javascript/gflib.js

@@ -34,7 +34,7 @@ Fun.prototype.show = function (prec) {
 		var s = this.name;
 		var cs = this.args;
 		for (var i in cs) {
-			s += " " + cs[i].show(1);
+		        s += " " + (isUndefined(cs[i]) ? "undefined" : cs[i].show(1));
 		}
 		if (prec > 0 && cs.length > 0) {
 			s = "(" + s + ")" ;