server : fix first message identification (#13634)

server : fix first message identification (#13634)

* server : fix first message identification

When using the OpenAI SDK (https://github.com/openai/openai-node/blob/master/src/lib/ChatCompletionStream.ts#L623-L626) we noticed that the expected assistant role is missing in the first streaming message. Fix this by correctly checking for the first message.

Co-authored-by: Piotr Stankiewicz <redacted>
Signed-off-by: Dorin Geman <redacted>
* server : Fix checks for first role message for stream=True

Co-authored-by: Piotr Stankiewicz <redacted>
Signed-off-by: Dorin Geman <redacted>
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Signed-off-by: Dorin Geman <redacted>
Co-authored-by: Piotr Stankiewicz <redacted>