Fix FTPS upload failure: !DATA ERROR 0 receiving on data socket

Don't treat CRYPT_ERROR_COMPLETE (-24) as a socket error during upload since it's an indication that the remote closed the connection and is the normal "end of file/transfer" indicator, not an error. 'rd' is already 0 in this case, so no need to set at all (since recv() returns 0 upon disconnect and that's what we're emulating here).

Fixes issue #309 reported by Jas Hud.