Fixed display of hidden fields on image add view

Same as #668 but for the old image add view

wagtail/wagtailimages/templates/wagtailimages/images/add.html

@@ -20,7 +20,11 @@
             {% csrf_token %}
             <ul class="fields">
                 {% for field in form %}
-                    {% include "wagtailadmin/shared/field_as_li.html" with field=field %}
+                    {% if field.is_hidden %}
+                        {{ field }}
+                    {% else %}
+                        {% include "wagtailadmin/shared/field_as_li.html" with field=field %}
+                    {% endif %}
                 {% endfor %}
                 <li><input type="submit" value="{% trans 'Save' %}" /></li>
             </ul>