all: change optional to result of io (#16075)

examples/vweb/vweb_assets/vweb_assets.v

@@ -17,7 +17,7 @@ fn main() {
 	mut app := &App{}
 	app.serve_static('/favicon.ico', 'favicon.ico')
 	// Automatically make available known static mime types found in given directory.
-	os.chdir(os.dir(os.executable()))?
+	os.chdir(os.dir(os.executable()))!
 	app.handle_static('assets', true)
 	vweb.run(app, port)
 }