core&ui: fix contestTimer on duration contest (#576)

packages/hydrooj/src/handler/problem.ts

@@ -371,6 +371,7 @@ export class ProblemDetailHandler extends ContestDetailBaseHandler {
         };
         if (this.tdoc && this.tsdoc) {
             const fields = ['attend', 'startAt'];
+            if (this.tdoc.duration) fields.push('endAt');
             if (contest.canShowSelfRecord.call(this, this.tdoc, true)) fields.push('detail');
             this.response.body.tsdoc = pick(this.tsdoc, fields);
         }