postfix: don't try to deploy undefined virtual aliases

postfix/tasks/main.yml

@@ -103,6 +103,7 @@
   template:
     src: virtual.j2
     dest: /etc/postfix/virtual
+  when: virtual_aliases is defined or postfix_virtual_domains|count > 0
   notify:
     - postmap virtual
   tags:

postfix/templates/main.cf.j2

@@ -84,7 +84,9 @@ tls_ssl_options = NO_COMPRESSION
 
 alias_maps = cdb:/etc/aliases
 alias_database = cdb:/etc/aliases
+{% if virtual_aliases is defined or postfix_virtual_domains|count > 0 %}
 virtual_alias_maps = cdb:/etc/postfix/virtual
+{% endif %}
 
 {% if postfix_virtual_domains|count > 0 %}
 virtual_mailbox_domains = {{ postfix_virtual_domains | join(", ") }}