Role access on note header is empty (and shows a "dash") for non-member of a project

As seen in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13291#note_40444696:

The access level for the person is 0 which makes the condition - if access = note_max_access_for_user(note) pass but Gitlab::Access.human_access(access) returns nil, which print nothing in the HTML.