ChatTongyi reasoning_content fix (#30694)

- **Description:** Small fix for `reasoning_content` key
- **Issue:** #30689

Author: keenborder786

libs/community/langchain_community/chat_models/tongyi.py

@@ -731,7 +731,7 @@ def _stream(
             if (
                 choice["finish_reason"] == "null"
                 and message["content"] == ""
-                and message["reasoning_content"] == ""
+                and message.get("reasoning_content", "") == ""
                 and "tool_calls" not in message
             ):
                 continue