fix：无数据时处理；

src/renderer/src/components/choose-textbook/third.vue

@@ -163,6 +163,10 @@ const handleNodeClick = (data,node) => {
 onMounted(() => {
   titleName.value = `${useStore.user.edustage}-${useStore.user.edusubject}`
   treeLoading.value = true
+  //存在查看无课程的情况，两秒后关闭loading框
+  setTimeout(() => {
+    treeLoading.value = false
+  },2000)
 })
 //监听数据变化
 watch(() => useThird,() => {

src/renderer/src/components/choose-textbook/third/index.vue

@@ -34,6 +34,7 @@ const getSubject = (value) => {
   const currentIndex = gradeList.findIndex(item => item.value === value)
   getSubjects({stage:value}).then(res => {
     if(res.code === 200){
+      if(res.data.length === 0) return
       subjectList.value = res.data.map(item => {
         return {
           ...item,