Actor.ts: updated .clone() method to test for non-null collider prior to attempting to clone.
Added test 'can be cloned with null collider; to ActorSpec.ts

This fixes issue reported in discord on 1/23/25:
https://discord.com/channels/1195771303215513671/1195779955611672598/1332073907213308055

Issue: 
![image](https://github.com/user-attachments/assets/ba3a2698-9a20-4dd0-a4f9-6f927bd01569)