[FIX] web: fix crash on editable list view when moving over a RO field

This is a forward-port of commit https://github.com/odoo/odoo/commit/970387f91fea0cb47404612f7d519ffba2c9ad3b



In editable list view, moving to next cell using TAB key crash when the
following field is becoming read-only (i.e non-focusable) and an onchange()
event is triggered.

Consider an editable tree view like this:

<form>
   <field name="o2m" onchange="1">
       <tree>
          <field name="description"/>
          <field name="date" attrs="{'readonly': [('description', '!=', False)]}"/>
          <field name="type"/>
       </tree>
   </field>
</form>

1. Edit 'description'
2. Issue a TAB keypress before 'date' becomes read-only
It will crash while calling getSelectionRange() on an empty element.

opw-2523630

closes odoo/odoo#71163

X-original-commit: 2a880a8020b55b692505846e9626359fe019dbdb
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>
Signed-off-by: Anh Thao PHAM <kitan191@users.noreply.github.com>