Add missing include to avoid compile error on windows

Change-Id: If338b41e416362fc36da25b16f119187a358206c
Reviewed-on: https://gerrit.libreoffice.org/11617
Reviewed-by: Matúš Kukan <matus.kukan@collabora.com>
Tested-by: Matúš Kukan <matus.kukan@collabora.com>