Fix gossip menu item overflow

[Tralenor]

closes #118

How to Test:
use this code to verify server doesn't crash after attempting to add more than 32 GossipMenuItems

local function hello(event, player, object)
    for n = 1, 40, 1 do
        player:GossipMenuAddItem(1, "Text "..n, 20124, n)
        print("added: "..n)
    end
    player:GossipSendMenu(0, object, 0)
end

RegisterCreatureGossipEvent(20124, 1, hello)

(Code copied from @55Honey in the issue linked above)

Expected Output in world-server console:

[Tralenor]

thanks for fixing the codestyle!

[55Honey]

Thank you for the fix!