Fix feature flag-gated game rules not having their defaults overriden

[EnnuiL]

Bad news! Since they are filtered from the initial game rules in the first place, you don't override the gated game rules in the first place, so you have to override those specific ones later!

The good news is that only one of them is affected, but the bad news is: it's the minecart speed game rule (a.k.a. haha minecart go vroom); so a fix is important anyway