Clicking on "Unlock"-button, sometimes shows page "404 - Not Found"

[jrief]

How to reproduce:

• Enable locking for the site (DJANGOCMS_VERSIONING_LOCK_VERSIONS = True).
• Someone else edits a page and publishes that page.
• Then he edits that page again, but he does not publish it. This keeps the page locked by him.
• I open the published page with the toolbar enabled.
• On the right, now there is a button named "Unlock".
• If I click on that button, error "404 - Not Found" is raised.

After analizing this, it turns out that the link behind the "Unlock"-button points onto the published page. This then results in the 404 - Not Found exception.

Unlocking a page can also be performed in the Versioning Admin List View. Here a list of page versions is rendered, but only the current version with state=DRAFT offers an unlock button. And from here, unlocking works as intended.

By applying this patch, unlocking a page should work as expected. However, I'm unsure if this is the right approach.

[fsbraun]

@jrief Just for clarification: The button should not be shown on the published page, right? Or, do you think the unlock button should unlock the draft version (and not try the published one)? (The latter would require a check if there is a draft version to unlock.)