fix onboarding bugs

app/inventory/api/engine/warehouse.php

@@ -4,7 +4,12 @@
     require '../../../assets/utils/classes/WarehouseManager.php';
 
     $wh = new WarehouseManager($pdo2, $company_id);
-    $answer['output']  = $wh->getWarehouseListAll();
-    $answer['success'] = 1;
+    $answer['output'] = $wh->getWarehouseListAll();
+    if (empty($answer['output'])) {
+        $answer['success'] = 0;
+        $answer['message'] = 'No warehouse found. Please go to <b>Inventory → Warehouse</b> to create your first warehouse before using this page.';
+    } else {
+        $answer['success'] = 1;
+    }
     exit(json_encode($answer));
 ?>