shows add booth link only for not assigned booths

app/views/admin/poll/booth_assignments/_search_booths_results.html.erb

@@ -25,10 +25,12 @@
           <%= booth.location %>
         </td>
         <td class="text-center">
+          <% unless @poll.booth_ids.include?(booth.id) %>
             <%= link_to t("admin.poll_booth_assignments.index.add_booth"),
                           admin_poll_booth_assignments_path(@poll, booth_id: booth.id),
                           method: :post,
                           class: "button hollow" %>
+          <% end %>
         </td>
       </tr>
       <% end %>