Feature flags: Handle logged-out users better.

If specific user accounts were allowed to use a feature, logged-out
users would cause the feature flag check to fail because
UnloggedUser.name exists but raises NotImplementedError.  This makes the
feature-world return None for user if no user is logged in.

Author: spladug

r2/r2/config/feature/world.py

@@ -37,7 +37,8 @@ def get_safe(o, key, default=None):
             return default
 
     def current_user(self):
-        return self.get_safe(c, 'user')
+        if c.user_is_loggedin:
+            return self.get_safe(c, 'user')
 
     def current_subreddit(self):
         site = self.get_safe(c, 'site')