Callbacks passed to functions implemented in Erlang as `erl_func` in the
likes were not updating state correctly.

For example, imagine the following Lua program

```lua
globalVar = { a = 1 }

function modify_global()
  globalVar['b'] = 2
end

external_call(modify_global)

return globalVar
```

`external_call` is a function implemented in Erlang as

```erlang
ExternalFun = fun([Fun], S) ->
    {FunRef, NewState1} = luerl_new:encode(Fun, S),
    io:format("Function ref: ~p~n", [FunRef]),

    {ok, Res, NewState2} = luerl_new:call(FunRef, [], NewState1),
    {Res, NewState2}
end,

State = luerl_new:init(),
{ok, [], State1} = luerl_new:set_table_keys_dec([<<"external_call">>], ExternalFun, State),
```

This program returns

```erlang
% Expected
[[{<<"a">>, 1}, {<<"b">>, 2}]]

% Actual
[[{<<"a">>, 1}}]]
```

- [X] Write a test case that reproduces the problem
- [ ] Fix the root cause