Fix VS2012 compile error
Fix VS2012 compile error

otris/ews-cpp,m-Schlitzer/ews-cpp,bkircher/ews-cpp,m-Schlitzer/ews-cpp,otris/ews-cpp,otris/ews-cpp,otris/ews-cpp,bkircher/ews-cpp,m-Schlitzer/ews-cpp,bkircher/ews-cpp