We don't check if a page already exists on page creation

Reproduction steps

1. Create a page A
2. Create a page A.B
3. Click on new page
4. set B as the page name
5. Select A as the parent
6. click on create

Expected

The user is warned that the new page already exist

Actual

The user is moved to the existing page, in edit mode

Result of the same scenario in XWiki: