Fix IsAlive throwing if entity is None

src/gaemstone.ECS/Entity.cs

@@ -19,7 +19,7 @@ public unsafe readonly partial struct Entity<TContext>
 	public bool IsSome    => Value.IsSome;
 
 	public bool IsValid => EntityAccess.IsValid(World, this);
-	public bool IsAlive => EntityAccess.IsAlive(World, this);
+	public bool IsAlive => IsSome && EntityAccess.IsAlive(World, this);
 
 	public string? Name	  { get => EntityAccess.GetName(World, this);   set => EntityAccess.SetName(World, this, value); }
 	public string? Symbol { get => EntityAccess.GetSymbol(World, this); set => EntityAccess.SetSymbol(World, this, value); }