src: fix order of CHECK_NOT_NULL/dereference

`ASYNC_THROW_IF_INSUFFICIENT_PERMISSIONS` may dereference
`req_wrap_async`, so `CHECK_NOT_NULL(req_wrap_async)` should be used
before and not after.

PR-URL: #59487
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <richard.lau@ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>

Author: tniessen

src/node_file.cc

@@ -1633,12 +1633,12 @@ static void Unlink(const FunctionCallbackInfo<Value>& args) {
 
   if (argc > 1) {  // unlink(path, req)
     FSReqBase* req_wrap_async = GetReqWrap(args, 1);
+    CHECK_NOT_NULL(req_wrap_async);
     ASYNC_THROW_IF_INSUFFICIENT_PERMISSIONS(
         env,
         req_wrap_async,
         permission::PermissionScope::kFileSystemWrite,
         path.ToStringView());
-    CHECK_NOT_NULL(req_wrap_async);
     FS_ASYNC_TRACE_BEGIN1(
         UV_FS_UNLINK, req_wrap_async, "path", TRACE_STR_COPY(*path))
     AsyncCall(env, req_wrap_async, args, "unlink", UTF8, AfterNoArgs,