Fix chitchat lost context (#1828)

Co-authored-by: luowei <glpat-EjySCyNjWiLqAED-YmwM>
Co-authored-by: crazywoola <427733928@qq.com>
Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

api/core/memory/read_only_conversation_token_db_buffer_shared_memory.py

@@ -27,7 +27,7 @@ class ReadOnlyConversationTokenDBBufferSharedMemory(BaseChatMemory):
         # fetch limited messages desc, and return reversed
         messages = db.session.query(Message).filter(
             Message.conversation_id == self.conversation.id,
-            Message.answer_tokens > 0
+            Message.answer != ''
         ).order_by(Message.created_at.desc()).limit(self.message_limit).all()
 
         messages = list(reversed(messages))