Fix 500 for labels page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/labels/_label.html.haml

-- frequency = @project.issues.tagged_with(label.name).count
 %li
-  %span{class: "label #{label_css_class(label.name)}"}
-    %i.icon-tag
-  - if frequency.zero?
-    %span.light= label.name
-  - else
-    = label.name
-  .pull-right
-    - unless frequency.zero?
-      = link_to project_issues_path(label_name: label.name) do
-        = pluralize(frequency, 'issue')
-        = "»"
+  = render_colored_label(label)