Can't enable sandbox mode

[Bertaz]

Same as #99

Save files created with sandbox mode disabled, give an error when trying to enable it Save: Galactic Shack.sav.gz

Error:

Uncaught Error: GameObject 0 has no id.
    at new t (utils.ts:16)
    at Object.t.replaceGameObject (utils.ts:139)
    at modify-difficulty.ts:63
    at Object.t.tryModifySaveGame (utils.ts:27)
    at t.default (modify-difficulty.ts:41)
    at utils.ts:12
    at Array.reduce (<anonymous>)
    at utils.ts:11
    at redux.js:459
    at t.default (reducer.ts:27)
```</details>

[RoboPhred]

Interesting. Game object 0 is typically the general info about the save file and it typically has an id to be looked up by. Good news is this should be straitforward to work out. I will download and inspect the save next weekend and figure out what the game is doing now.