core: bug fix

packages/hydrooj/package.json

@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.1.8",
+    "version": "3.1.9",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",

packages/hydrooj/src/handler/problem.ts

@@ -256,7 +256,7 @@ export class ProblemDetailHandler extends ProblemHandler {
         }
         if (ddoc.langs) {
             (this.pdoc.config as ProblemConfig).langs = intersection(
-                this.response.body.pdoc.config.langs || ddoc.langs.split(','),
+                (this.pdoc.config as ProblemConfig).langs || ddoc.langs.split(','),
                 ddoc.langs.split(','),
             );
         }