core: handle image download cache

packages/import-qduoj/handler.ts

@@ -122,7 +122,7 @@ class ImportQduojHandler extends Handler {
     async post({ domainId }) {
         if (!this.request.files.file) throw new ValidationError('file');
         const stat = await fs.stat(this.request.files.file.path);
-        if (stat.size > 128 * 1024 * 1024) throw new BadRequestError('File too large');
+        if (stat.size > 128 * 1024 * 1024) throw new ValidationError('file', 'File too large');
         await this.ImportFromFile(domainId, this.request.files.file.path);
         this.response.redirect = this.url('problem_main');
     }