l10n_it_vat_registries bug if no entry_order selected

[FrancescoGermani]

Module

l10n_it_vat_registries

Describe the bug

Quando si stampano registri IVA lasciando vuoto il campo "Inserire Ordine" (nome tecnico "entry_order") si riceve il seguente errore:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 1652, in _serve_db
    return service_model.retrying(self._serve_ir_http, self.env)
  File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 133, in retrying
    result = func()
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 1679, in _serve_ir_http
    response = self.dispatcher.dispatch(rule.endpoint, args)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 1883, in dispatch
    result = self.request.registry['ir.http']._dispatch(endpoint)
  File "/usr/lib/python3/dist-packages/odoo/addons/base/models/ir_http.py", line 154, in _dispatch
    result = endpoint(**request.params)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 734, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/dataset.py", line 46, in call_button
    action = self._call_kw(model, method, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/dataset.py", line 33, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/api.py", line 468, in call_kw
    result = _call_kw_multi(method, model, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/api.py", line 453, in _call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/parts/project_addons/OCA/l10n-italy/l10n_it_vat_registries/wizard/print_registro_iva.py", line 96, in print_registro
    move_ids = self._get_move_ids(wizard)
  File "/parts/project_addons/OCA/l10n-italy/l10n_it_vat_registries/wizard/print_registro_iva.py", line 79, in _get_move_ids
    order = MAPPING[wizard.entry_order]

KeyError: False

To Reproduce

Affected versions: 16.0

Steps to reproduce the behavior:

1. Andare in contabilità e provare a stampare registri IVA lasciando vuoto il campo di cui sopra

Expected behavior
Non dovrebbe essere possibile lasciare il campo vuoto