保存考试时，无默认enable，由后台决定

src/api/examwork-exam.js

@@ -32,7 +32,7 @@ export function saveExam({
   code = "",
   createId = 0,
   createTime = "",
-  enable = 0,
+  enable = "",
   enableIpLimit = 0,
   endTime = "",
   entryAuthenticationPolicy = "",