[BFCL] 当 tool_calls 为 [] 时,函数调用解析器返回空响应

Describe the issue _parse_query_response_FC does not correctly handle API responses where message.tool_calls exists but is an empty list ([]). In that case, the current implementation returns model_responses=[] instead of falling back to message.content.

ID datapoint

1. Datapoint/Model Handler permalink:
2. Issue: Function-calling parser returns empty model_responses when tool_calls=[]
3. Gorilla repo commit #: 6ea57973c7a6097fd7c5915698c54c17c5b1b6c8