- Create an account of type current asset
- Add him a Sales Tax and a Purchase Tax
- Create invoice
- Add a line
- Remove the taxes from this line
- Change the account to the one you created

=> A purchase tax is applied to the line.
It should not happen, so we prevent it.

closes odoo/odoo#115196

Signed-off-by: Quentin De Paoli <qdp@odoo.com>