[FIX] website_sale: add conditions to make sure partner's name exists

Reproduction:
1. Install Event, Sales, Website, Contacts
2. Login as Admin, create a new portal user 123, set the password as 123
3. Go to Contacts, find the created user, add a shipping address, leave
the name blank
4. Open another tab login as the portal user, place an order
5. At the Address step, Edit the billing address, change the name from
empty to “Test Name”, click next
5. An error is thrown cause the new name is not equal to empty value

Fix: this fix aimed the conditions we have in the previous PR: https://github.com/odoo/odoo/pull/111708
This change will allow the user to add a name for shipping address at
checkout.Without the fix, if you
change the name of a shipping address, it won’t be able to get through.
This is because of how we manage the shipping address, e.g. shipping
address is managed as child partners. For shipping address, the check
can_edit_vat is always false. See here: https://github.com/odoo/odoo/blob/14.0/addons/portal/models/res_partner.py
Another check, e.g. if shipping is being edited, is added to make sure
name/email can be changed for delivery address. For internal user, the
editing of shipping address is not blocked because of the `share` check.
But the same condition is used to ensure the consistency in case we
change how the shipping address is managed in the future.

Note: if the data is '' for name for example, the pre-process will
convert it to `False`. Thus the edge case that `'' != False` doen't
exist anymore

Related PR: https://github.com/odoo/odoo/pull/111708



opw-3126325

closes odoo/odoo#128146

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>