OXMLSubDocument: copy PrintWhenGroupChange, too

Change-Id: If6a5d9a50f5d600b96faebc51b9798a8e63eec49
Reviewed-on: https://gerrit.libreoffice.org/9501
Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Lionel Elie Mamane <lionel@mamane.lu>