MINOR Better error checking in SiteTreeNode javasceript

git-svn-id: svn://svn.silverstripe.com/silverstripe/open/modules/cms/trunk@105679 467b73ca-7a2a-4603-9d3b-597d59a354a9

Author: chillu

javascript/LeftAndMain.Tree.js

@@ -421,7 +421,7 @@ SiteTreeNode.prototype = {
 		this.TreeNode.initialize(options);
 		if(this.className && this.className.match(/class\-([^\s]*)/)) {
 			var klass = RegExp.$1;
-			if(siteTreeHints && siteTreeHints[klass]) {
+			if(typeof siteTreeHints != 'undefined' && siteTreeHints[klass]) {
 				this.hints = siteTreeHints[klass];
 				this.dropperOptions = { 
 					accept : (this.hints.allowedChildren && (this.className.indexOf('nochildren') == -1))