Address remaining issue with #451

This PR updates the fix for #451, where `zip_source_filep_create` fails on Windows with a large zip archive. 1. Assign `_fseeki64` to `zip_os_fseek`. `zip_os_seek` is not used anywhere in the code and `HAVE__SEEK64` is not defined so assuming this was just an error. 2. `_ftelli64` needs to be assigned to `zip_os_ftell` so 64 bit version is invoked.