Cancelling streaming returns error `"error, <nil>"`

[OrkhanAlikhanov]

Describe the bug
After cancelling the context passed to CreateChatCompletionStream, stream.Recv() returns "error, " error. Debugging shows that it happens in these lines:

go-openai/stream_reader.go

Lines 63 to 71 in c4273cb

	for {
	rawLine, readErr := stream.reader.ReadBytes('\n')
	if readErr != nil || hasErrorPrefix {
	respErr := stream.unmarshalError()
	if respErr != nil {
	return nil, fmt.Errorf("error, %w", respErr.Error)
	}
	return nil, readErr
	}

After cancellation rawLine, readErr := stream.reader.ReadBytes('\n') returns io.EOF error but then stream.unmarshalError() returns *openai.ErrorResponse that wraps *openai.APIError which wraps nil value.

Expected behavior
It should propagate io.EOF properly

Screenshots/Logs
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Environment (please complete the following information):

• go-openai version: v1.40.1
• Go version: 1.24.5
• OpenAI API version: v1
• OS: macOS

Additional context
Add any other context about the problem here.