优化性能，优化折线图和柱状图的大数据绘制，重构代码

Runtime/Internal/SerieLabelPool.cs

@@ -57,6 +57,7 @@ namespace XCharts
 
         public static void Release(GameObject element)
         {
+            if (element == null) return;
             ChartHelper.SetActive(element, false);
             if (!Application.isPlaying) return;
             if (!m_ReleaseDic.ContainsKey(element.GetInstanceID()))