fix: prevent error on admin orders list when customer is deleted

Add null check on ``$order->customer`` in ``OrdersDataTable`` to display
"Client supprimé" instead of crashing when the related customer record
no longer exists.

app/Datatables/Admin/Shop/OrdersDataTable.php

@@ -35,7 +35,9 @@ class OrdersDataTable extends DataTable
                 return $order->created_at->format('d/m/Y H:i:s');
             })
             ->editColumn('customer.last_name', function (Order $order) {
-                return $order->customer->last_name.' '.$order->customer->first_name;
+                return $order->customer
+                    ? $order->customer->last_name.' '.$order->customer->first_name
+                    : 'Client supprimé';
             })
             ->editColumn('payment_type', function (Order $order) {
                 return InvoicePayments::getPaymentType($order->payment_type);