fix 开考失败的错误提示

src/features/OnlineExam/StartExamModal.vue

@@ -267,13 +267,21 @@ async function enterExam() {
         courseName: encodeURIComponent(newRes.courseName),
       });
     } catch (error) {
-      // console.log(error);
+      // console.log(error, error.response, error.isAxiosError);
       if ("isAxiosError" in <any>error) {
         const ne = <AxiosError>error;
-        const desc: string = ne.response?.data?.desc;
+        const jsonRes = JSON.parse(<string>ne.response?.data ?? "null");
+        const desc: string = jsonRes.desc;
         if (desc) {
           $message.error(desc);
           logger({ cnl: ["server"], act: "开考失败", dtl: desc });
+        } else {
+          logger({
+            cnl: ["server"],
+            act: "开考失败",
+            dtl: "开考失败，并且无错误消息",
+            possibleError: error,
+          });
         }
       } else {
         logger({