Correct preprint server counting in choose server template

submissions/templates/submissions/submit_choose_preprint_server.html

@@ -23,7 +23,7 @@
     <div class="row">
       <div class="col-md-6">
 	<h2 class=highlight>Step 3</h2>
-	{% if preprint_servers|length > 1 %}
+	{% if preprint_server_list|length > 1 %}
 	  <h3>Which preprint server do you wish to use for your {% if thread_hash %}re{% endif %}submission?</h3>
 	  <p>SciPost's own preprint server is always available.
 	    We however strongly encourage you to use your field's customary