This commit updates (writer).Writer() method in S3 storage driver to
handle the case where an append is attempted to a zer-size content.
S3 does not allow appending to already committed content, so we are
optiing to provide the following case as a narrowed down behaviour:
Writer can only append to zero byte content - in that case, a new S3
MultipartUpload is created that will be used for overriding the already
committed zero size content.
Appending to non-zero size content fails with error.
Co-authored-by: Cory Snider <corhere@gmail.com>
Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>
4baddbc608