Fix LabelTTF initial content size, texture rect not correct issue

Author: pandamicro

cocos2d/core/labelttf/CCLabelTTF.js

@@ -133,9 +133,7 @@ cc.LabelTTF = cc.Sprite.extend(/** @lends cc.LabelTTF# */{
         this._renderCmd._setFontStyle(this._fontName, fontSize, this._fontStyle, this._fontWeight);
         this.string = strInfo;
         this._renderCmd._setColorsString();
-        if (this._string) {
-            this._renderCmd._updateTexture();
-        }
+        this._renderCmd._updateTexture();
         this._setUpdateTextureDirty();
 
         // Needed for high dpi text.

cocos2d/core/labelttf/CCLabelTTFCanvasRenderCmd.js

@@ -402,6 +402,7 @@ cc.LabelTTF._firsrEnglish = /^[a-zA-Z0-9ÄÖÜäöüßéèçàùêâîôû]/;
     proto._updateTexture = function () {
         this._dirtyFlag = this._dirtyFlag & cc.Node._dirtyFlags.textDirty ^ this._dirtyFlag;
         var node = this._node;
+        node._needUpdateTexture = false;
         var locContentSize = node._contentSize;
         this._updateTTF();
         var width = locContentSize.width, height = locContentSize.height;