The multipart upload complete endpoint returns 200 with an empty body,
but rclone tried to decode that body as JSON, failed with EOF and
retried until the retries ran out, so every upload failed even though
the server had actually completed it.
Fixed by not attempting to decode the response body.
This was a regression introduced in
a4972de505 shade: retry server errors instead of failing the transfer
which started treating the JSON decode error as fatal where previously
it was accidentally ignored.