AttachmentResource.update incorrectly requires version+1

PUT to rest/api/content/<id>/child/attachment/<attachmentid> only updates attachment metadata - it doesn't change the attachment content nor create a new version, which is correct.

However it requires that the version in the post is <currentversion+1> (it rejects <currentversion> with a 409 Conflict error), which is incorrect, since the metadata on <currentversion> is updated, and no <currentversion+1> is created.