Prevent the user from converting messages and warn them, if there are no puzzles

app/views/contests/show.html.slim

@@ -50,6 +50,10 @@
       .row.mt-5
         .col
           h4 = t("messages.plural").capitalize
+      - if !@puzzles.size
+        .row
+          .col.alert.alert-danger
+            | You first need to add a puzzle before converting messages to completions
       table.table.table-striped.table-hover
         thead
           tr
@@ -69,8 +73,12 @@
               td
                 = message.text
               td
+                - if @puzzles.size
                   a.btn.btn-sm.btn-secondary href=contest_message_convert_path(@contest, message) style="white-space: nowrap;"
                     = t("helpers.buttons.add_completion")
+                - else
+                  a.btn.btn-sm.btn-secondary.disabled href=contest_message_convert_path(@contest, message) style="white-space: nowrap;"
+                    = t("helpers.buttons.add_completion")
               td
                 = link_to t("helpers.buttons.delete"), contest_message_path(@contest, message), data: { turbo_method: :delete }, class: "btn btn-sm btn-danger"
   .col-6