Throw in EntityPath.From if entity is None

src/gaemstone.ECS/EntityPath.cs

@@ -52,6 +52,9 @@ public class EntityPath
 
 	public static unsafe EntityPath From(World world, Entity entity)
 	{
+		if (entity.IsNone) throw new ArgumentException(
+			"entity is Entity.None", nameof(entity));
+
 		var parts = new List<byte[]>(32);
 
 		do {