Fix: Completion AttributeError: 'list' object has no attribute 'get' (#3999)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Co-authored-by: lizheng@ssc-hn.com <lizheng@ssc-hn.com>

api/apps/conversation_app.py

@@ -187,6 +187,8 @@ def completion():
                 return d.get(k1, d.get(k2))
 
             for ref in conv.reference:
+                if isinstance(ref, list):
+                    continue
                 ref["chunks"] = [{
                     "id": get_value(ck, "chunk_id", "id"),
                     "content": get_value(ck, "content", "content_with_weight"),