fix(性能测试): 修复导出性能测试报告图错乱的问题

--bug=1015370 --user=刘瑞斌 【性能测试】导出报告后查看pdf报告，显示内容不对 https://www.tapd.cn/55049933/s/1212803

frontend/src/common/js/utils.js

@@ -271,7 +271,7 @@ export function exportPdf(name, canvasList) {
       let blankHeight = a4Height - currentHeight;
 
       if (leftHeight > blankHeight) {
-        if (blankHeight < 200) {
+        if (blankHeight < 300) {
           pdf.addPage();
           currentHeight = 0;
         }
@@ -285,10 +285,10 @@ export function exportPdf(name, canvasList) {
           leftHeight -= occupation;
           position -= occupation;
           //避免添加空白页
-          // if (leftHeight > 0) {
-          // pdf.addPage();
-          // currentHeight = 0;
-          // }
+          if (leftHeight > 0) {
+            pdf.addPage();
+            currentHeight = 0;
+          }
         }
       } else {
         pdf.addImage(pageData, 'JPEG', 0, currentHeight, imgWidth, imgHeight);