library/roles/nginx/tasks/nginx-virtualhosts.yml: Fix a problem with a new variable that's undefined by default.

nginx/tasks/nginx-virtualhosts.yml

@@ -1,12 +1,12 @@
 ---
 - name: Install the nginx virtualhost files
   template: src=nginx-virthost.j2 dest=/etc/nginx/sites-available/{{ item.virthost_name }} owner=root group=root mode=0444
-  with_items: '{{ nginx_virthosts }}'
+  with_items: '{{ nginx_virthosts | default(omit) }}'
   notify: Reload nginx
   tags: [ 'nginx', 'virtualhost' ]
 
 - name: Enable the nginx virtualhosts
   file: src=/etc/nginx/sites-available/{{ item.virthost_name }} dest=/etc/nginx/sites-enabled/{{ item.virthost_name }} state=link
-  with_items: '{{ nginx_virthosts }}'
+  with_items: '{{ nginx_virthosts | default(omit) }}'
   notify: Reload nginx
   tags: [ 'nginx', 'virtualhost' ]