Change approval: reviewer cannot approve his own change

Description

Steps to reproduce:

1. Edit the approval sequence of a content item, such as an Alloy Track page.
2. Add Editor1 as reviewer of step #1.
3. Check "Prevent users from approving their own changes".
4. Save.
5. Editor1 starts a change approval corresponding the content. For example, he changes the expiration date.
6. Editor1 views the change details and approves the changes.

Expected:
Editor1 is unable to approve his own change since "Prevent users from approving their own changes" was checked

Actual:
Editor1 gets a message "This command is not available for approval".