Zillion: ensure 1st sphere not empty

[beauxq]

What is this fixing or adding?

Zillion could rarely have no locations in 1st sphere

https://github.com/ArchipelagoMW/Archipelago/actions/runs/6191949342/job/16811145959

How was this tested?

unit tests (in both zilliandomizer package and AP)

and playing through an AP game

[black-sliver]

MakeFailure leads to rerolling the room/layout?

[beauxq]

MakeFailure leads to rerolling the room/layout?

Yes, for that room.

If you roll a seed with the room gen option on zilliandomizer (not Archipelago), you can get a good idea of what is happening.
It displays in the console a period . for each time it rerolls a room. It often rerolls 10-20 times per room to get something that works. This change adds a very low probability of reroll on 1 room.

Note that the room gen is not run in unit tests, since it requires information from the rom.
So only the changes in src/zilliandomizer/randomizer.py affect the unit test failures. (The vanilla room layout already has the property ensured by the room gen changes.)