何かのはずみでインデント幅が極端に小さくなってしまうことがあったのを修正

git-svn-id: http://www.cozmixng.org/repos/piro/treestyletab/trunk@1613 599a83e7-65a4-db11-8015-0010dcdd6dc2

content/treestyletab/treestyletabbrowser.js

@@ -1814,7 +1814,7 @@ TreeStyleTabBrowser.prototype = {
 
 		var oldMargin = this.levelMargin;
 		var indent    = (oldMargin < 0 ? this.baseLebelMargin : oldMargin ) * nest;
-		var maxIndent = b.mTabContainer.childNodes[0].boxObject[this.invertedSizeProp] * 0.33;
+		var maxIndent = b.mTabContainer.boxObject[this.invertedSizeProp] * 0.33;
 
 		var marginUnit = Math.max(Math.floor(maxIndent / nest), 1);
 		if (indent > maxIndent) {