svx::frame::Style::Set(): typo: subtract if it's _not_ 0
svx::frame::Style::Set(): typo: subtract if it's _not_ 0

(regression from 2c91cb08d65cd35fa8ef6eaca3677aa82fb58cbe)

Change-Id: I9803b630067de26503fceb32b5d7c6a46f352a7a

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