Remove back link from 404 error page (#23222967)

I've kept it for 400/403/500/csrffail for now, because they also have a
"try again" link. Yes, both things have browser buttons, but they make
it a *little* clearer to technical users what one could to next, and
especially on csrffail, "step back" is always possible and possibly actually
helpful.

src/pretix/base/templates/404.html

@@ -8,9 +8,6 @@
         <h1>{% trans "Not found" %}</h1>
         <p>{% trans "I'm afraid we could not find the the resource you requested." %}</p>
         <p>{{ exception }}</p>
-        <p class="links">
-            <a id='goback' href='#'>{% trans "Take a step back" %}</a>
-        </p>
         {% if request.user.is_staff and not staff_session %}
             <form action="{% url 'control:user.sudo' %}?next={{ request.path|add:"?"|add:request.GET.urlencode|urlencode }}" method="post">
                 <p>

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

@@ -1,14 +1,14 @@
 {% extends "pretixpresale/event/base.html" %}
 {% load i18n %}
 {% load bootstrap3 %}
-{% block title %}{% trans "Resend order links" %}{% endblock %}
+{% block title %}{% trans "Resend order link" %}{% endblock %}
 {% block custom_header %}
     {{ block.super }}
     <meta name="robots" content="noindex, nofollow">
 {% endblock %}
 {% block content %}
     <h2>
-        {% trans "Resend order links" %}
+        {% trans "Resend order link" %}
     </h2>
     <p>
         {% blocktrans trimmed %}

src/pretix/presale/views/order.py

@@ -1510,7 +1510,10 @@ class OrderChangeMixin:
                             'max_count': iao.max_count,
                             'iao': iao,
                             'items': [i for i in items if not i.require_voucher],
-                            'items_missing': {k: v for k, v in current_addon_products_missing.items() if v},
+                            'items_missing': {
+                                k: v for k, v in current_addon_products_missing.items()
+                                if v and k[0].category_id == iao.addon_category_id
+                            },
                         })
 
         return positions