Another quick patch: AI (usually) won't walk into the aircraft anymore + 1 other

Hey team,

Added a navigation obstacle to the aircraft, so AI (usually) won't walk into the helicopter anymore. It's been a day 1 issue that I never managed to fix because I wasn't looking at the problem right. There may still be rare instances of them bumping into you, because I had to compromise between making them walk around, and making it possible to still run them over and be attacked at short range by them. Also fixed the invincibility cheat, which was calling you a cheater but not actually doing anything of benefit.

Thanks for your support!

-Raulboy