Before this commit, when sending multiples invoices by email in batch,
if one of these invoices was for a customer without an email address,
these wasn't sent and the user didn't have any feedback about this.
Now, before the user send the emails a warning is shown with the list of
invoices that can't be sent by email.
opw-2002350
closesodoo/odoo#33753
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>