[fix] checkbox ids

searx/templates/search.html

     <div>
     {% for category in categories %}
         <div class="checkbox_container">
-            <input type="checkbox" name="category_{{ category }}" {% if category in selected_categories %}checked="checked"{% endif %} /><label for="checkbox_{{ category }}" class="cb"></label><label for="checkbox_{{ category }}">{{ category }}</label>
+            <input type="checkbox" id="checkbox_{{ category|replace(' ', '_') }}" name="category_{{ category|replace(' ', '_') }}" {% if category in selected_categories %}checked="checked"{% endif %} /><label for="checkbox_{{ category }}" class="cb"></label><label for="checkbox_{{ category }}">{{ category }}</label>
         </div>
     {% endfor %}
     </div>