fix: 修复下载链接处理函数的bug

src/modules/conversation-dialog/format-dialog-answer-custom-markdown-str.js

@@ -81,6 +81,10 @@ export function formatRefferenceFlag(answer) {
  * @param {string} file_id
  */
 export function formatFileDownloadStr(file_name, file_url, file_id) {
+  if (!file_name || !file_url) {
+    return '';
+  }
+
   let real_url = file_url.replace('//', '/');
   real_url = file_url.replace('/./', '/');
   real_url = file_url.replace('./', '/');