[FIX] website_forum: users count requires super-user permissions
[FIX] website_forum: users count requires super-user permissions

Introduced at 893d7fa8643192aec817478effa44c55d3c1ebc4
during new API conversion: missing `sudo()`.

Fixes #6578

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