[FIX] account_voucher: unreconcile with deleted journal items

This is possible to unreconcile and then remove journal
items associated to `account.voucher.line`.

When it's done, the voucher is within a corrupted state,
with debits and credits lines without journal item, which
is required.

Because the journal item of this line is empty,
while required, this is no longer possible to use
the "Unreconcile" button, because the form is invalid.

In order to allow to unreconcile a posted customer/supplier
payments with missing journal items, we set
the journal items as required only when the payment
is within the `draft` stage.

opw-667232