Emscripten - Closing the game through the menu does not display the end session screen and display a warning

[Mimigris]

Reproducing: Go on https://easyrpg.org/play/master/, select Exit on the title screen, or open the settings menu and select <Exit game>.

Instead of displaying the "It is now safe to turn off your browser." message, the screen will turn black and an error will happen in the console.