[BUG] Incorrect methodology for `is_menu_item_dropdown` simple tag

**Describe the bug**
A clear and concise description of what the bug is.

This code block:

@register.simple_tag
def is_menu_item_dropdown(value):
return \
len(value.get('sub_links', [])) > 0 or \
(
value.get('show_child_links', False) and \
len(value.get('page', []).get_children().live()) > 0
)

What if you actually hit the case where `value.get('page', [])` defaults to a list? Then `.get_children().live()` is being called on an object which doesn't have these methods. Also, probably shouldn't inline all of this for readability despite the faster evaluation.

One simple fix:

@register.simple_tag
def is_menu_item_dropdown(value):
has_sub_links = len(value.get('sub_links', [])) > 0
show_child_links = value.get('show_child_links', False)
page_has_children = False
if has_sub_links or show_child_links: # No need to evaluate the below if this case fails...
page = value.get('page')
if page is not None:
page_has_children= len(page.get_children().live()) > 0
return has_sub_links or (show_child_links and page_has_children)

This is also assuming you still want to be verbose with the evaluation into booleans here.

Busca en el repositorio la etiqueta simple is_menu_item_dropdown e inspecciona cómo se usa su valor page. Reproduce el caso en el que page está ausente o tiene un valor predeterminado incorrecto y, después, verifica que la etiqueta evita llamar a métodos de page cuando su valor no es una página, al tiempo que conserva el comportamiento de los subenlaces y los enlaces secundarios.

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