core: unset record contest attr when deleting contest

packages/hydrooj/package.json

@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.10.3",
+    "version": "3.10.4",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",

packages/hydrooj/src/handler/contest.ts

@@ -137,6 +137,7 @@ export class ContestDetailHandler extends Handler {
         const tdoc = await contest.get(domainId, tid);
         if (!this.user.own(tdoc)) this.checkPerm(PERM.PERM_EDIT_CONTEST);
         await contest.del(domainId, tid);
+        await record.updateMulti(domainId, { domainId, contest: tid }, undefined, undefined, { contest: '' });
         await TaskModel.deleteMany({
             type: 'schedule', subType: 'contest', domainId, tid,
         });