refactor(single-instance): improve userdata ptr handling (#2453)

* fix(single-instance): fix null pointer dereference panic on Windows

* fmt

plugins/single-instance/examples/vanilla/src-tauri/build.rs

@@ -3,5 +3,5 @@
 // SPDX-License-Identifier: MIT
 
 fn main() {
-  tauri_build::build()
+    tauri_build::build()
 }