Fixed potential crash during state validation

https://forum.zdoom.org/viewtopic.php?t=57116

The problem was caused by missing state label in conjunction with incomplete class

actor A : ArmorBonus
{
    Inventory.ForbiddenTo "Missing"
}

actor B : Pistol
{
    states
    {
        TNT1 A 0
        Loop
    }
}

src/info.h

@@ -344,7 +344,7 @@ public:
 	bool OwnsState(const FState *state)
 	{
 		auto i = ActorInfo();
-		return state >= i->OwnedStates && state < i->OwnedStates + i->NumOwnedStates;
+		return i != nullptr && state >= i->OwnedStates && state < i->OwnedStates + i->NumOwnedStates;
 	}
 
 	PClassActor *GetReplacement(bool lookskill=true);