s3: CopyObject return http Status 400 Bad Request for non-existing source
s3: CopyObject return http Status 400 Bad Request for non-existing source

fix https://github.com/chrislusf/seaweedfs/issues/2306

chrislusf/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs