上传失败，防御型编程(iview)

src/features/OfflineExam/OfflineExamUpload.vue

@@ -175,7 +175,7 @@ export default {
       this.loadingStatus = false;
       console.log(error);
       this.$Message.error({
-        content: file.desc || "上传失败",
+        content: (file && file.desc) || "上传失败",
         duration: 15,
         closable: true,
       });