Issue was caused by _wstat returning EOVERFLOW error because of file size didn't fit into stat structure which was using long datatype. The idea of this patch is to use _wstat64 and _stat64 structure which is capable storing 64bit file sizes. Made it a typedef for stat structure used by BLI_stat function in order to make code easier to follow and avoid ifdefs all over the place. Additionally solved issue with BLI_exists which was wrongly returning False in cases destination file is larger then 4GB.