[FIX]web_tour:avoid unnecessary traceback
[FIX]web_tour:avoid unnecessary traceback

In certain case, a non blocking traceback pops-up.
It happens when the page loads, if the dom is modified
before the tour has been fully loaded.

Theorical steps to reproduce:
- Open a page with an active tour
- Trigger any domain change before the tip-dot is loaded

On every change in the DOM, the MutationObserver tries
to update the page. If the tip-dot has not been loaded yet,
it will try to update the position of a non-existing element.
In that case, we simply ignore it. The update will be called
anyway when the tip-dot has finished his loading.

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closes odoo/odoo#34199

Signed-off-by: Nicolas Martinelli (nim) <771435c469f83f6aa9c405ac5e1ed06314a94f2d@odoo.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo