Fix: Python SDK retrieve document_name is empty (#12062)

### What problem does this PR solve?

https://github.com/infiniflow/ragflow/issues/12056

### Type of change

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

sdk/python/ragflow_sdk/modules/chunk.py

@@ -33,6 +33,7 @@ class Chunk(Base):
         self.create_timestamp = 0.0
         self.dataset_id = None
         self.document_name = ""
+        self.documnet_keyword = ""
         self.document_id = ""
         self.available = True
         # Additional fields for retrieval results
@@ -46,6 +47,11 @@ class Chunk(Base):
                 res_dict.pop(k)
         super().__init__(rag, res_dict)
 
+        #for backward compatibility
+        if not self.document_name:
+            self.document_name = self.documnet_keyword
+
+
     def update(self, update_message: dict):
         res = self.put(f"/datasets/{self.dataset_id}/documents/{self.document_id}/chunks/{self.id}", update_message)
         res = res.json()