core: 修复rating计算错误的问题

packages/hydrooj/src/script/rating.ts

@@ -120,7 +120,7 @@ export async function calcLevel(domainId: string, report: Function) {
 
 async function runInDomain(id: string, isSub: boolean, report: Function) {
     const info = await domain.getUnion(id);
-    info.union.push(id);
+    if (info) info.union.push(id);
     const udict: ND = {};
     const deltaudict: ND = {};
     const domainId = info ? { $in: info.union } : { $exists: false };