Perk_RandomDecide should throw an objerror instead of causing a runaway

[MotoLegacy]

Describe your suggestion
If a map maker is not using perk_random properly to the point where machines are trying to spawn perks when there are not any available slots left, there should be a verbose objerror to report this and also not crash the level.

[MotoLegacy]

Docs page should also be updated to add note that you cannot spawn duplicate machines via perk_random.