creating enemy vehicles on rough terrain may cause createmaintarget to crash

[longtimegamer]

steps to reproduce

• select a maintarget with high number of vehicles and lots of mountains
• sometimes the search for a flat position fails in fn_spawnvehicle
• maintarget setup fails

the search should exit after 99 attempts, my bug

[longtimegamer]

https://github.com/Xeno69/Domination/pull/490