Deleting any but the first of multiple combats causes the first combat to enter a bad state

[aaclayton]

Originally in GitLab by @Fyorl

Originally reported by kamcknig#8494 https://discord.com/channels/170995199584108546/848968607526551592/859224317615013898

On a world with no modules activated, I seem to have found a bug with combat.

1. Create a combat
2. Add combatant
3. Create a new combat
4. Delete the new combat
5. Attempt to delete combatant from original combat

Once this happens, no combatants can be added or removed from the broken combat.

EDIT 1: In addition, once the combat is broken, a refresh does not fix the issue. The combat must be deleted and recreated

EDIT 2: Furthermore, it appears it is only encounter 1 that is broken. Meaning that if you create five combats, and delete any combat at all then after the deletion the combat that is now at position 1 is always broken. The other combats can have combatants added/removed from them