[FIX] warning: Blocking messages with PO
[FIX] warning: Blocking messages with PO

Before the fix, it was possible to create a PO with a vendor who had
a Blocking Message set on.

opw:656875

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