`model` is missing in first streaming response.

[Eason0729]

openai api must contain choices, id, model in each sse response.

And here is a sample of first sse response

{
  "choices": [],
  "created": 0,
  "id": "",
  "prompt_filter_results": [
    {
      "content_filter_results": {
        "hate": {
          "filtered": false,
          "severity": "safe"
        },
        "self_harm": {
          "filtered": false,
          "severity": "safe"
        },
        "sexual": {
          "filtered": false,
          "severity": "safe"
        },
        "violence": {
          "filtered": false,
          "severity": "safe"
        }
      },
      "prompt_index": 0
    }
  ]
}