fix: 修复字符串替换的bug

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

@@ -53,6 +53,10 @@ export function formatRefferenceString(refference, field_key) {
 }
 
 export function formatRefferenceFlag(answer) {
+  if (!answer) {
+    return '';
+  }
+
   let cur_text = answer;
 
   cur_text = cur_text.replace(/##\d\$\$/g, function (match, index, full) {