fix: prevent error 500 on search with no results

``getArticlesToSell()`` returned ``false`` when no articles matched,
causing ``collect(false)`` to produce ``[false]``. The view then
iterated over that single-element array and tried to access array
offsets on a boolean value.

app/Repositories/Shop/Articles.php

@@ -204,7 +204,7 @@ class Articles
             ksort($data);
         }
 
-        return $data ?? false;
+        return $data ?? [];
     }
 
     public static function getDataForSale($article)