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MINOR: [C++] Row wise conversion example fix (#13648)

This example should print the expected rows.

Lead-authored-by: zhangchaoming.1999@bytedance.com <zhangchaoming.1999@bytedance.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Co-authored-by: moses <zhangchaoming.1999@bytedance.com>
Co-authored-by: zhang chaoming <72908278+ZhangChaoming@users.noreply.github.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>