fixes fails if icinga2_objects arent defined which is the default

roles/icinga2/tasks/objects.yml

@@ -8,7 +8,7 @@
 - name: collect all config objects in play vars
   set_fact:
     tmp_objects: "{{ tmp_objects| default([]) + lookup('list', icinga2_objects) }}"
-  when: vars['icinga2_objects'][icinga2_config_host] is not defined
+  when: icinga2_objects is defined and vars['icinga2_objects'][icinga2_config_host] is not defined
 
 - icinga2_object:
     args: "{{ item }}"