Send to review error after fresh database install.

Prereq.: Reinstall studio demo database before test.

Steps:
1. Go to Content / Content structure.
2. Select e.g. Blog post content item.
3. Click Edit.
4. Click Send for review.
5. Choose reviewer.
6. Click Confirm.
Actual result: User stays in Content Editor, error is displayed in browser console (400, bad request).
Expected result: Content is sent for review, user leaves Content Editor.

Remarks: On version 1.3 (opposed to master above) an error message is displayed in browser: "An error occurred while saving the draft".

Backend investigation: It happens when trying to send to review published content. New draft version is created on send to review action and new version id is returned from backend. But this draft version is ignored on frontend and AJAX request to sent-to-review use published version id which lead to error (it's not possible to review published version).