Small follow-up fix for [6254] - `DefaultPermissionPolicy` needs to return `True` or `None` so that it doesn't break the chain. 
Small follow-up fix for [6254] - `DefaultPermissionPolicy` needs to return `True` or `None` so that it doesn't break the chain. 

Without the fix, the default `LegacyAttachmentPolicy` would never get called as defalt option is `permission_policies = DefaultPermissionPolicy, LegacyAttachmentPolicy`.

git-svn-id: 0d96b0c1a6983ccc08b3732614f4d6bfcf9cbb42@6259 af82e41b-90c4-0310-8c96-b1721e28e2e2

rbaumg/trac,rbaumg/trac,rbaumg/trac,rbaumg/trac