[FIX] account: default company currency
[FIX] account: default company currency

On a payment form, the company currency is obtained from the journal.
This means that as long as no journal has been selected, no company
currency is defined and the payment difference is wrongly calculated.

This fix uses as company currency the currency of the user's company if
no journal is chosen, which should be a safe choice and lead to a
correct calculation of the payment difference.

opw-658177

bplancher/odoo,storm-computers/odoo,sysadminmatmoz/OCB,Elico-Corp/odoo_OCB,laslabs/odoo,ygol/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,microcom/odoo,hip-odoo/odoo,sysadminmatmoz/OCB,optima-ict/odoo,storm-computers/odoo,bplancher/odoo,storm-computers/odoo,stephen144/odoo,Elico-Corp/odoo_OCB,stephen144/odoo,ygol/odoo,optima-ict/odoo,stephen144/odoo,bplancher/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,dfang/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,laslabs/odoo,sysadminmatmoz/OCB,microcom/odoo,hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo,microcom/odoo,sysadminmatmoz/OCB,sysadminmatmoz/OCB,stephen144/odoo,optima-ict/odoo,storm-computers/odoo,laslabs/odoo,ygol/odoo,optima-ict/odoo,sysadminmatmoz/OCB,laslabs/odoo,storm-computers/odoo,hip-odoo/odoo,stephen144/odoo,microcom/odoo,bplancher/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,sysadminmatmoz/OCB,bplancher/odoo,microcom/odoo,Elico-Corp/odoo_OCB,ygol/odoo,dfang/odoo,optima-ict/odoo,dfang/odoo,stephen144/odoo,hip-odoo/odoo,storm-computers/odoo,microcom/odoo,optima-ict/odoo,ygol/odoo