fix delete button

Author: nikmel2803

src/backend/views/pages/form.twig

@@ -64,7 +64,7 @@
 
     <div class="writing-buttons">
       {% include 'components/button.twig' with {label: 'Save changes', name: 'js-submit-save', icon: 'check'} %}
-      {% if page._id is not empty %}
+      {% if toString(page._id) is not empty %}
           {% include 'components/button.twig' with {label: 'Delete doc', name: 'js-submit-remove', icon: 'trash', style: 'warning'} %}
       {% endif %}
     </div>