Update hooks.lua to fix crash when leaving lobby

[Xzyer]

When a player leaves a multiplayer lobby (or an opponent disconnects), Entropy crashes with:

[SMODS entr "lib/hooks.lua"]:1169: bad argument #1 to 'pairs' (table expected, got nil)

The crash occurs during the transition from the multiplayer lobby state back to the main menu. SMODS.get_card_areas('jokers') returns a non-nil table of area objects, but those area objects have a nil .cards field because the jokers area has not been fully initialized yet during this game-state transition.

Affected locations in lib/hooks.lua:
- Line ~1169 — inside create_card function (the primary crash site)
- Line ~2170 — inside add_tag function
- Line ~3138 — inside interest calculation function

All three iterate over _joker_areas = SMODS.get_card_areas('jokers') and then call pairs(a.cards) without checking if .cards is nil.

Reproduction:
1. Join a multiplayer game lobby with Entropy installed
2. Leave the lobby (or have an opponent disconnect)
3. Game crashes on transition back to main menu

Proposed fix: Add nil guards around a.cards in all three locations:

Before:

 for i, a in pairs(SMODS.get_card_areas('jokers')) do
        for _, c in pairs(a.cards) do

After:

local _joker_areas = SMODS.get_card_areas('jokers')
if _joker_areas then
    for i, a in pairs(_joker_areas) do
        if a.cards then   <-- guard added
            for _, c in pairs(a.cards) do