Guests are allowed to delete XWikiServer[Name] documents

Steps to reproduce:

1. Create 2 new subwikis: test & test2
2. Log-out
3. Hover over Home and click "Wiki Index"; you'll see both your subwikis
4. Hover over Home and click "Document Index"
5. Click on XWikiServerTest
6. Delete the document; you'll get a lot of

   [XWiki Solr index thread] ERROR .a.DefaultAuthorizationManager - Failed to load rights for user [Public] on [test:XWiki.XWikiSkinsSheet]

   errors in the console

Now when you hover over Home and click "Wiki Index" you'll see only the Test2 subwiki. If you manually enter the address for the Test subwiki logged in as an Admin there's no menu for administering the subwiki.