Fix procfile and attachment in event nore

Procfile

 web: bundle exec unicorn_rails -p $PORT
-worker: bundle exec sidekiq -q post_receive,mailer,system_hook,project_web_hook,common,default,gitolite
+worker: bundle exec sidekiq -q post_receive,mailer,system_hook,project_web_hook,common,default,gitlab_shell

app/views/events/event/_note.html.haml

@@ -25,9 +25,10 @@
   %span.event-note
     = markdown truncate(event.target.note, length: 70)
     - note = event.target
-    = link_to note.attachment.url, target: "_blank", class: 'note-file-attach' do
-      - if note.attachment.image?
-        = image_tag note.attachment.url, class: 'note-image-attach'
-      - else
-        %i.icon-paper-clip
-        = note.attachment_identifier
+    - if note.attachment.url
+      = link_to note.attachment.url, target: "_blank", class: 'note-file-attach' do
+        - if note.attachment.image?
+          = image_tag note.attachment.url, class: 'note-image-attach'
+        - else
+          %i.icon-paper-clip
+          = note.attachment_identifier