Fix ‘Back’ link from first step of fix one off

If you skip past the templates page (because you don’t have the edit
permission) but then click back you end up in a loop which redirects you
to the page you’re already on.

This commit makes sure that you’re sent back a step further, so you
don’t get stuck in that loop.

app/main/views/templates.py

@@ -29,6 +29,7 @@ from app.template_previews import TemplatePreview, get_page_count_for_letter
 from app.utils import (
     email_or_sms_not_enabled,
     get_template,
+    should_skip_template_page,
     user_has_permissions,
 )
 
@@ -49,11 +50,7 @@ page_headings = {
 @user_has_permissions()
 def view_template(service_id, template_id):
     template = service_api_client.get_service_template(service_id, str(template_id))['data']
-    if (
-        current_user.has_permissions('send_messages') and
-        not current_user.has_permissions('manage_templates', 'manage_api_keys') and
-        template['template_type'] != 'letter'
-    ):
+    if should_skip_template_page(template['template_type']):
         return redirect(url_for(
             '.send_one_off', service_id=service_id, template_id=template_id
         ))