Optionally make unbound recursive if no forward is configured

unbound/templates/unbound.conf.j2

@@ -6,8 +6,10 @@ server:
 	access-control: {{i}} allow
 	{% endfor %}
 
+{% if unbound_upstream_hosts is defined and unbound_upstream_hosts %}
 forward-zone:
 	name: "."
 	{% for i in unbound_upstream_hosts %}
 	forward-addr: {{i}}
 	{% endfor %}
+{% endif %}