Merge branch 'admin_notes_fix' into 'master'

Admin area: doesn't show a note when it's empty

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/12636

See merge request !133

app/views/admin/users/index.html.haml

@@ -74,7 +74,7 @@
           - else
             %i.fa.fa-user.cgreen
           = link_to user.name, [:admin, user]
-          - if user.note
+          - if user.note.present?
             = link_to "#", { "data-toggle" => "tooltip", title: user.note, class: "user-note"} do
               = icon("sticky-note-o cgrey")
           - if user.admin?