Add conditional for wg_additional_host_keys

roles/wireguard/templates/wg.conf.j2

@@ -69,6 +69,7 @@ Endpoint = {{host}}:{{wireguard_port}}
 {% endif %}
 {% endfor %}
 
+{% if wg_additional_host_keys is defined %}
 {% for host in wg_additional_host_keys %}
 [Peer]
 # {{hostvars[host].name}}
@@ -76,3 +77,4 @@ PublicKey = {{hostvars[host].public_key}}
 AllowedIPs = {{hostvars[host].wireguard_ip}}/32
 PersistentKeepalive = {{hostvars[host].wireguard_persistent_keepalive}}
 {% endfor %}
+{% endif %}