When a new Landing Page is created and the user clicks on the toggle to switch into preview mode, instead of the current Landing Page draft preview, its parent is used.

Steps to reproduce
1. Clean installation of eZ Platform 3.1
2. In Content structure, when viewing Welcome to eZ Platform Enterprise Edition click on "Create" button, and select "Landing Page".
3. Select the default template, click on "Create Draft
4. Click on "View edit switcher" to switch into preview mode.

Result
Page Builder will open Welcome to eZ Platform Enterprise Edition in preview mode.

Expected result
Page Builder will open the current Landing Page draft in preview mode.