FRED Asserts with scripting and async calls

I was trying to use async to essentially force a script to init after a downstream script where the file hierarchy kinda made naming for priority tricky and ran into this. Basically if you use on async call with the onFrameExecutor, it expects a game state which of course is invalid in FRED. It triggers the assert in `gamesequence.cpp` on line 437 because FRED is not in a game state.

I don't know a whole lot about the async code so I didn't try anything really but I'm wondering if we could either create a GS_STATE_FRED = -1 enumeration for the game states or perhaps if `Fred_running` at line 437, return some kind of preset value since FRED can't really have other states. I'm not sure if there's other places the onFrameExecutor might break down in FRED, though.