Added a simple guard that prevents an exception being thrown on application exit

[minimallyexceptional]

Locally I kept getting the same exception over and over when closing the program.

It turns out that the server log entry was still firing slightly after the app had quit, leaving webContents undefined.

Just needed a simple guard return out once the app has been exited.

[frankhale]

Great catch! Thank you so much for fixing this.

[minimallyexceptional]

No problem! Keep up the good work, your roguelikes look awesome!