[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) <nim@odoo.com>

addons/web_tour/static/src/js/tip.js

@@ -146,6 +146,7 @@ var Tip = Widget.extend({
     },
     _reposition: function () {
         if (this.tip_opened) return;
+        if (!this.$el) return;
         this.$el.removeClass("o_animated");
 
         // Reverse left/right position if direction is right to left