Merge branch 'no-todo-badge-on-zero' into 'master'

Don't show the Todo count if there aren't any Todos.

When there are 0 Todos, the Todos icon still had the blue badge with a "0" in it, which made me think I had a new Todo left. This makes it less annoying.

Follow-up on !4077.

**Before:**

![Screen_Shot_2016-05-10_at_9.36.57_PM](/uploads/e0dfafae01692286096606c3251f0997/Screen_Shot_2016-05-10_at_9.36.57_PM.png)

**After:**

![Screen_Shot_2016-05-10_at_10.01.02_PM](/uploads/30a8bafe8f54862418eb4045e5777a9a/Screen_Shot_2016-05-10_at_10.01.02_PM.png)

cc: @jschatz1 @rspeicher 

See merge request !4113

app/views/layouts/header/_default.html.haml

@@ -27,6 +27,7 @@
             %li
               = link_to dashboard_todos_path, title: 'Todos', data: {toggle: 'tooltip', placement: 'bottom', container: 'body'} do
                 = icon('bell fw')
+                - unless todos_pending_count == 0
                   %span.badge.todos-pending-count
                     = todos_pending_count
             - if current_user.can_create_project?