fix(测试用例): 计划Tab页空数据时报错提示

--bug=1044837 --user=宋昌昌 【测试用例】用例详情-用例未关联计划-点击测试计划标签报错 https://www.tapd.cn/55049933/s/1559719

frontend/src/views/case-management/caseManagementFeature/components/tabContent/tabTestPlan.vue

@@ -215,8 +215,10 @@
     (val) => {
       if (val) {
         const selectedPlanIds: (string | undefined)[] = propsRes.value.data.map((e) => e.testPlanId) || [];
+        if (selectedPlanIds && selectedPlanIds.length > 0) {
           getStatistics(selectedPlanIds);
         }
+      }
     },
     {
       deep: true,