fix cairo canvas regression - do not access polygon points outside range
fix cairo canvas regression - do not access polygon points outside range

(cherry picked from commit a898a8cb077c05b1085da8254e66f61aa265b7dc)

Signed-off-by: Thorsten Behrens <22ffb59efaabdc5a02f4f136cd2eba491d4acfb6@novell.com>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core