oracleobjectstorage: upload empty streams without multipart

OCI rejects a multipart completion request with no parts. Probe unknown-size
streams through a buffered reader and use a regular upload when the stream is
empty. Peek preserves a non-empty stream for the selected upload path.

(cherry picked from commit e85836d4c7)
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f