Privilege escalation (PR) from account via custom skins support

Steps to reproduce:

1. As a user without edit, script or admin right, add an object of class `XWiki.XWikiSkins` to your profile. Name it whatever you want and set the Base Skin to `flamingo`.
2. Add an object of class `XWikiSkinFileOverrideClass` and set the path to `macros.vm` and the content to ```
   #macro(mediumUserAvatar $username)
     #resizedUserAvatar($username 50)
     $services.logging.getLogger('Skin').error("I got programming: $services.security.authorization.hasAccess('programming')")
   #end
   ```
3. Back to your profile, click `Test this skin`. Force a refresh, just in case.

Expected result:

The logs should be empty, or display "I got programming: false" if the user has script rights.

Actual result:

An error "ERROR Skin - I got programming: true" is logged.