fix bug on multipart upload
fix bug on multipart upload

aliyun/oss-ftp,aliyun/oss-ftp,johnkeepmoving/oss-ftp,johnkeepmoving/oss-ftp,johnkeepmoving/oss-ftp,aliyun/oss-ftp,aliyun/oss-ftp,johnkeepmoving/oss-ftp,johnkeepmoving/oss-ftp,johnkeepmoving/oss-ftp,aliyun/oss-ftp,johnkeepmoving/oss-ftp,aliyun/oss-ftp,aliyun/oss-ftp,johnkeepmoving/oss-ftp