WifiManager: fix crash if no wifi device found (#23701)

selfdrive/ui/qt/offroad/wifiManager.cc

@@ -226,8 +226,10 @@ uint WifiManager::getAdapterType(const QDBusObjectPath &path) {
 }
 
 void WifiManager::requestScan() {
+  if (!adapter.isEmpty()) {
     asyncCall(adapter, NM_DBUS_INTERFACE_DEVICE_WIRELESS, "RequestScan", QVariantMap());
   }
+}
 
 QByteArray WifiManager::get_property(const QString &network_path , const QString &property) {
   return call<QByteArray>(network_path, NM_DBUS_INTERFACE_PROPERTIES, "Get", NM_DBUS_INTERFACE_ACCESS_POINT, property);