fix: Don't display None comments

src/meal_manager/templates/event.html

@@ -123,7 +123,7 @@
                 <td>{{ reg.num_adult_meals }}</td>
                 <td>{{ reg.num_children_meals }}</td>
                 <td>{{ reg.num_small_children_meals }}</td>
-                <td>{{ reg.comment }}</td>
+                <td>{{ reg.comment | default("") }}</td>
                 <td><a href="/event/{{event.id}}/registration/{{reg.household_id}}/delete"><i class="bi bi-trash"></i></a></td>
             </tr>
             {% endfor %}