[Crash] Saving the game after an AIscript start_town removed missing guards may crash

[BoneHorror]

start_town removes missing guards on first use for the given AI player; when combined with an AI that may train missing guard units quickly and a map where guards are bulk removed by triggers (like xZ6, Fury of the Swarm for the intro sequence) AND Zerg AIs being able to train units out of nonstandard buildings (for example Hydras from Nydus Canals) this may result in aise panic crash when the Player attempts to Save some time after the removal.
Doesn't seem to occur without AISE, didn't manage to reproduce it without Nydus Hydra training
Repro (seems to need uedaip exe unfortunately, or mod everything written above instead):

1. Launch a modded exe with necessary changes (add dat reqs for training to something the AI already owns in the map)
2. Start Fury of the Swarm from the BW Zerg campaign menu
3. After the intro sequence plays out, wait a few seconds after the AI starts so that it starts training defenseuse etc. units
4. Attempt to save
   Repro at least 5/10, might depend on whether a nydus/non-larva building is used to train?
   

[neivv]

Investigation so far~

This is caused by ai having guards in training when the guard ai is removed from the player. Saving resets all non-player guard ai objects to zero which makes this trigger easier, but is not strictly necessary.

Generally this could've happened before iwth the old guard ai share bug (guard dying while another guard for same ai is being trained) - i think aise's fix for that is good enough, as it makes sure that any guard being trained does not have the ai object owned by an unit.

But the second place where guards get removed is when start_town is used and ai has 0 existing towns, all guards get deleted.

So to fix aise should either

1. Reimplement start_town, probably nicest results but quite lot of work due to the choke point calculation code. Would be nice to have that softcoded though.
2. Hook before start_town, would require samase api changes for aiscript opcode hooking, ugh
3. Check each frame that no guard being trained uses freed guard ai

3rd one is simplest to implement, and the performance is probably perfectly fine, but due to spendreq changes this is no longer common crash so holding it off in case i get to doing 1st one instead.