Remove indent and reduce bloat with link_to_if

See

 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16900#note_60163789
 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16900#note_60164324

app/views/projects/_stat_anchor_list.html.haml

 - anchors = local_assigns.fetch(:anchors, [])
 
-- if anchors.size > 0
-  %ul.nav
+- return unless anchors.any?
+%ul.nav
   - anchors.each do |anchor|
     %li
-        - if anchor.link
-          = link_to anchor.link, class: anchor.enabled ? 'stat-link' : "btn btn-#{anchor.class_modifier || 'missing'}" do
-            = anchor.label
-        - else
-          %span.stat-text
-            = anchor.label
+      = link_to_if anchor.link, anchor.label, anchor.link, class: anchor.enabled ? 'stat-link' : "btn btn-#{anchor.class_modifier || 'missing'}" do
+        %span.stat-text= anchor.label