index out of bound when streaming with IncludeUsage as true

[aryanshridhar]

To Reproduce
When streamed chat completion with request having StreamOptions defined as -

req := openai.ChatCompletionRequest{
	Model:     openai.GPT3Dot5Turbo,
	Messages: []openai.ChatCompletionMessage{
		{
			Role:    openai.ChatMessageRoleUser,
			Content: "Lorem ipsum",
		},
	},
	StreamOptions: &openai.StreamOptions{IncludeUsage: true},
	Stream:        true,
}

breaks for last chunk-

panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
main.main()
	/Users/aryan/Desktop/go-openai/examples/completion/main.go:60 +0x4b0
exit status 2

Expected behavior
The condition to his the EOF error and stop the streaming process.

Environment (please complete the following information):

• go-openai version: master
• Go version: go version go1.22.3 darwin/arm64
• OpenAI API version: v1

[aryanshridhar]

For anyone facing issue till this is fixed, can rely on FinishReason explicitly and return if present

response, err := stream.Recv()
isOver := response.Choices[0].FinishReason

if errors.Is(err, io.EOF) || len(isOver) > 0 {
	return
}