fix build with MSVC
fix build with MSVC

error C2664: 'libetonyek::IWORKFormula::IWORKFormula(const boost::optional<unsigned int> &)': cannot convert argument 1 from 'int' to 'const boost::optional<unsigned int> &'

Change-Id: Iaa3de2d0ef8f960495e5d5afebb75c5063955177

LibreOffice/libetonyek,LibreOffice/libetonyek,LibreOffice/libetonyek