bug fixes

src/modules/student/lab/components/Exam.vue

@@ -19,6 +19,7 @@ const currentExam = computed(() => {
 
 // 考试平台 URL
 const examURL = computed(() => {
+  if (!currentExam.value) return ''
   return `${import.meta.env.VITE_EXAM_SHOW_URL}/exam/${currentExam.value?.exam_id}`
   // return `https://dev.ezijing.com:5173/exam/7003551966412406784?has_time=0&has_submit=0&has_save=1&show_answer=1`
 })