ipa/client: Deal better with unset IPA variables

Signed-off-by: Nils Philippsen <nils@redhat.com>

roles/ipa/client/tasks/common.yml

@@ -12,9 +12,10 @@
   changed_when: false
   loop: >-
     {{
-      ipa_server_user_groups
-      + (ipa_server_all_groups_hosts_dict | list | product(['sysadmin-main']) | list)
+      (ipa_server_user_groups | default([]))
+      + (ipa_server_all_groups_hosts_dict | default({}) | list | product(['sysadmin-main']) | list)
     }}
+  when: ipa_server_user_groups is defined or ipa_server_all_groups_hosts_dict is defined
 
 ## Rules specific to hosts, host groups