Fix: (Flat-screen versions) Back Buttons cause stacked UI! — MH-Zombie Steam update #1159255

Hey team, Apparently the back buttons on The Laboratory have been broken since the last patch and nobody's said anything until now. My apologies for not catching that myself, but it's fixed now! Also, for the VR version, my last change doesn't seem to have fixed the issue, so I'm still working on that. Thanks for your patience and support! -Raulboy