fixed got wrong Rect by Label::getBoundingBox.

cocos/2d/CCLabel.cpp

@@ -1364,6 +1364,13 @@ const Size& Label::getContentSize() const
     return Node::getContentSize();
 }
 
+Rect Label::getBoundingBox() const
+{
+    const_cast<Label*>(this)->getContentSize();
+
+    return Node::getBoundingBox();
+}
+
 void Label::listenToBackground(EventCustom *event)
 {
 #if CC_ENABLE_CACHE_TEXTURE_DATA

cocos/2d/CCLabel.h

@@ -243,6 +243,8 @@ public:
 
     virtual const Size& getContentSize() const override;
 
+    virtual Rect getBoundingBox() const;
+
     FontAtlas* getFontAtlas() { return _fontAtlas; }
     /** Listen "come to background" message
      It only has effect on Android.