fix: omit "Access rules" directives if no rules configured

When an access list was associated with a template which had users (items) but no rules (clients), a `deny all` directive was inserted to the config. This resulted in all requests, including those with valid credentials, being rejected due to the lack of any `allow` directive.

This commit wraps the access rule configuration inside of an if block, so the `deny all;` directive is only present when at least one rule is configured.

backend/templates/_access.conf

@@ -10,11 +10,13 @@
 
     {% endif %}
 
+    {% if access_list.clients.length > 0 %}
     # Access Rules: {{ access_list.clients | size }} total
     {% for client in access_list.clients %}
     {{client | nginxAccessRule}}
     {% endfor %}
     deny all;
+    {% endif %}
 
     # Access checks must...
     {% if access_list.satisfy_any == 1 or access_list.satisfy_any == true %}