[FIX] website_event_sale: avoid empty writes on product for each registration
[FIX] website_event_sale: avoid empty writes on product for each registration

The sale.order.line on_change returns related field
values that are not meant to be written on the line.
Removing them from the `values-to-be-written` avoids
the useless write() on product.product and the locking
problems that come with it under high concurrency
environments.

syci/OCB,ygol/odoo,bplancher/odoo,hip-odoo/odoo,stephen144/odoo,microcom/odoo,mkieszek/odoo,microcom/odoo,microcom/odoo,tvtsoft/odoo8,tvtsoft/odoo8,hip-odoo/odoo,optima-ict/odoo,mkieszek/odoo,dfang/odoo,laslabs/odoo,stephen144/odoo,hip-odoo/odoo,tvtsoft/odoo8,ygol/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,storm-computers/odoo,mkieszek/odoo,bplancher/odoo,syci/OCB,hip-odoo/odoo,mkieszek/odoo,syci/OCB,storm-computers/odoo,ygol/odoo,optima-ict/odoo,sysadminmatmoz/OCB,Elico-Corp/odoo_OCB,mkieszek/odoo,storm-computers/odoo,dfang/odoo,tvtsoft/odoo8,ygol/odoo,mkieszek/odoo,stephen144/odoo,laslabs/odoo,dfang/odoo,syci/OCB,sysadminmatmoz/OCB,storm-computers/odoo,syci/OCB,sysadminmatmoz/OCB,hip-odoo/odoo,syci/OCB,Elico-Corp/odoo_OCB,optima-ict/odoo,sysadminmatmoz/OCB,optima-ict/odoo,dfang/odoo,stephen144/odoo,laslabs/odoo,ygol/odoo,bplancher/odoo,Elico-Corp/odoo_OCB,ygol/odoo,microcom/odoo,tvtsoft/odoo8,ygol/odoo,sysadminmatmoz/OCB,bplancher/odoo,laslabs/odoo,dfang/odoo,sysadminmatmoz/OCB,Elico-Corp/odoo_OCB,dfang/odoo,hip-odoo/odoo,optima-ict/odoo,bplancher/odoo,optima-ict/odoo,storm-computers/odoo,storm-computers/odoo,sysadminmatmoz/OCB,microcom/odoo,laslabs/odoo,tvtsoft/odoo8,Elico-Corp/odoo_OCB,stephen144/odoo,stephen144/odoo,microcom/odoo,bplancher/odoo