[FIX] mail: automatic subscription of responsible
[FIX] mail: automatic subscription of responsible

Do not erase existing subscription with void subtypes.

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