[0.15.30] Crash on exit while in new game menu

[Zorky]

Minor bug: Factorio crashes when I try to close Factorio when the Resource settings window is open.

Steps to reproduce, 100% reproducible on my system:

1. Start Factorio
2. click Play
3. click New game
4. click Resource settings
5. Hit Alt-F4 with intent to close Factorio, or click the Red X in windowed mode.

Effect: Factorio Crashes, "Unexpected error occurred ..."
Expectation: Factorio closes gracefully.

[HanziQ]

Thank you for the report, fixed for the next version.