[FIX] web_editor: Cannot read property 'left' of undefined
[FIX] web_editor: Cannot read property 'left' of undefined

This issue happen for example on a full runbot when clicking with
shift + key pressed on a sale order not in an editable.

We can see that initial_data.rect is only defined in mousedown when the
click target is inside an editable block, hence it could lead to an
issue otherwise.

closes #11527

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