core: update vnode selection

packages/hydrooj/src/handler/problem.ts

@@ -126,6 +126,7 @@ export class ProblemMainHandler extends ProblemHandler {
         for (const pid of pids) {
             // eslint-disable-next-line no-await-in-loop
             const pdoc = await problem.get(domainId, pid);
+            if (!pdoc) continue;
             if (!this.user.own(pdoc, PERM.PERM_EDIT_PROBLEM_SELF)) this.checkPerm(PERM.PERM_EDIT_PROBLEM);
             // eslint-disable-next-line no-await-in-loop
             await problem.del(domainId, pid);