forgot a conditional in dokuwiki backup install

tasks/dokuwiki.yml

@@ -166,6 +166,7 @@
       dest: "{{ docroot }}"
       owner: "{{ lighttpd_user }}"
       group: "{{ lighttpd_group }}"
+    when: use_backup and backup_guard_present.matched == 0
 
   - name: add guard file to let ansible know backup is completed
     file: