Null-guard AreaInstance lookups in combat / death broadcasts

[CoreyRDean]

Summary

Six sites in GameServer.bb resolved Object.AreaInstance(actor\ServerArea) and immediately dereferenced AInstance\FirstInZone / AInstance\Spawned without checking the lookup succeeded. Object.X(handle) returns Null on a stale handle — typical trigger here is an actor mid-warp whose ServerArea was cleared before SetArea fully settled the new zone, or a zone-unload race against a script-spawned attack.

Sites

Site	Function	Behavior
KillActor:130-140	AI-death broadcast loop	Tell players in zone the AI died
KillActor:191-202	Zone linked-list removal	Detach the dead AI from FirstInZone chain
KillActor:204-207	Spawn-point counter	Decrement Spawned[SourceSP]
FireProjectile:227	Visual broadcast for ranged shots	Tell players to render the in-flight projectile
ActorAttack:303	Ranged-attack broadcast (CombatFormula <> 4)	Tell area about the ranged attack
ActorAttack:546	Melee-attack broadcast	Tell area about the melee attack

All six follow the same recovery: if AInstance is Null, skip the loop / counter update. The orphaned NextInZone pointers from a freed zone are dangling anyway — there's nothing to detach from, and no one to broadcast to. Authoritative damage / kill state still resolves on the server; only the visual / network broadcast is skipped.

Pattern reference

Established by the rcce2-packet-handler skill and recently documented in CLAUDE.md under "Handle-lookup Null discipline" (PR #145). This is the server-side application of the same Object.X(handle) guard pattern the client-side PR #144 added for PlayerTarget.

Out of scope (follow-up)

UpdateActorInstances at line 625+ has the same AInstance pattern at higher fanout (per-actor per-tick AInstance access for water damage, etc.). That surface needs a different shape of fix — skip the actor's entire tick, not just one broadcast — and lands in a separate PR.

Test plan

• compile.bat -t builds Server / Client / GUE / Project Manager cleanly.
• Force a kill of an actor whose ServerArea has been cleared mid-warp (e.g. a BVM script that calls KILLACTOR on an actor immediately after WARP). Server logs (well, doesn't crash) and the kill cleanup proceeds without the broadcast.
• Sanity: normal in-area combat still propagates attack and death packets.

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