stack/erp5: Fix postfix instanciation in non-relay mode

Empty values are considered not provided, so provide a template which
produces a file with a lone comment.

stack/erp5/buildout.hash.cfg

@@ -50,7 +50,7 @@ md5sum = f928b9dc99f7f970caadfe7dd6f95d34
 
 [template-postfix]
 filename = instance-postfix.cfg.in
-md5sum = 8f7bfca893a01c390df7a3dc9c2410e1
+md5sum = b1cdeb8fe02d47c093658b50afa7d6b9
 
 [template-postfix-master-cf]
 filename = postfix_master.cf.in

stack/erp5/instance-postfix.cfg.in

@@ -104,7 +104,7 @@ output = ${directory:etc-postfix}/sasl_passwd
 {% if relay -%}
 inline = {{ "{{ host }} {{ sasl_credential }}" }}
 {%- else -%}
-inline =
+inline = {{ dumps("# empty") }}
 {%- endif %}
 context =
     key host configuration:relayhost