core: fix bugs (#702)

packages/hydrooj/src/handler/contest.ts

@@ -473,6 +473,7 @@ export class ContestEditHandler extends Handler {
         if (beginAtMoment.isSameOrAfter(endAt)) throw new ValidationError('duration');
         const beginAt = beginAtMoment.toDate();
         const lockAt = lock ? moment(endAt).add(-lock, 'minutes').toDate() : null;
+        if (lockAt && contestDuration) throw new ValidationError('lockAt', 'duration');
         await problem.getList(domainId, pids, this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN) || this.user._id, true);
         if (tid) {
             await contest.edit(domainId, tid, {