This removes an "Unhandled execption in script... AtrributeError: 'NoneType' object has no attribute 'write'" error dialog that can pop up when the application is executed without anny stdout attached.
Context: This error was encountered by a Windows user when trying to open Electrum ABC while it was already running. In such a case the application prints "ok" (the return value of `server.gui(config_options)` to stdout. Luckily this error does not happen in a "normal" scenario (Electrum ABC started only once) every time the gui application is about to be closed , because the print call is preceded by `sys.exit(0)` . See the `electrum-abc::run_gui` function