XP actions still NPE every tick when per-skill XP multipliers are used

[MakeAsplashKira]

Follow-up to the previous XP report — still reproduces in 2.4.0 on PZ 42.20.4, Single Player.

The trigger

Sandbox option MultiplierConfig.GlobalToggle set to off (per-skill XP multipliers instead of
one global one). Its default is true, which is why this doesn't show up with default settings.

What happens

Any action wrapped by ExpActions.WrapUpdate throws on every update() tick — 500–1000 errors per
action:

Lua((MOD:The Only Cure)).action(ExpActions.lua:87)
    Lua((MOD:The Only Cure)).IterateTOCXp(ExpActions.lua:29)
    Lua((MOD:The Only Cure)).AddTOCXp(ExpActions.lua:86)
    Lua((MOD:The Only Cure)).update(ExpActions.lua:123)
java.lang.NullPointerException: Cannot invoke "zombie.SandboxOptions$SandboxOption.asConfigOption()" because the return value of "zombie.SandboxOptions.getOptionByName(String)" is null
    at zombie.characters.IsoGameCharacter$XP.AddXP(IsoGameCharacter.java:14269)

Why

With the global toggle off, AddXP looks up a per-skill multiplier by name:

xp *= Float.parseFloat(SandboxOptions.instance
    .getOptionByName("MultiplierConfig." + perk.getType())   // perk.toString() == perk id
    .asConfigOption().getValueAsString());

MultiplierConfig.* options exist only for the 36 vanilla skills. Side_L, Side_R and
ProstFamiliarity have none, so the lookup returns null.

This can't be fixed on the Lua side: addXp has a single 3-arg overload, and AddXPNoMultiplier
just calls back into the same code path. The option has to exist.

Fix

Add to 42/media/sandbox-options.txt (vanilla values are 0.0 / 1000.0 / 1.0):

option MultiplierConfig.Side_L
{
    type = double,
    min = 0.0,
    max = 1000.0,
    default = 1.0,
    page = MultiplierConfig,
    translation = TOC_MultiplierSide_L,
}

same for Side_R and ProstFamiliarity, plus the Sandbox_TOC_Multiplier* translation keys.