Allow to enter a voucher before choosing a subevent

src/pretix/presale/templates/pretixpresale/event/index.html

@@ -101,6 +101,12 @@
                     {{ frontpage_text|rich_text }}
                 </div>
             {% endif %}
+
+            {% if request.GET.voucher %}
+                <div class="alert alert-info">
+                    {% trans "Please select a date to redeem your voucher." %}
+                </div>
+            {% endif %}
         {% endif %}
 
         {% if subevent and "year" not in request.GET %}