feat: 修复初始进入时就开始下载图表图片

packages/extend-components/EC_HistoryView/src/SingleChart.js

@@ -78,7 +78,7 @@ const SingleChart = memo((props) => {
         return _option;
     }, [dataSource, smooth, curveCenter, chartType, predicateData]);
     useEffect(() => {
-        if (exportCanvas) {
+        if (exportCanvas.exportFlag) {
             const chart = chartRef.current?.getEchartsInstance?.();
             let a = document.createElement('a');
             a.href = chart.getDataURL('image/png');