[FIX] web_editor: prevent traceback on create and quick discard mailing

In mass_mailing:
1. Click CREATE
2. As soon as it appears, click "DISCARD"
3. Wait a little bit
-> A traceback appeared.

That is because wysiwyg was still busy starting and, in that process,
requested the window object of the iframe that was already removed.

closes odoo/odoo#84358

X-original-commit: 48ce4f0f834b55692e32868194a635b817c6ed13
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -1232,6 +1232,10 @@ const Wysiwyg = Widget.extend({
             const eventName = elem.dataset.eventName;
             let colorpicker = null;
             const mutex = new concurrency.MutexedDropPrevious();
+            if (!elem.ownerDocument.defaultView) {
+                // In case the element is not in the DOM, don't do anything with it.
+                continue;
+            }
             // If the element is within an iframe, access the jquery loaded in
             // the iframe because it is the one who will trigger the dropdown
             // events (i.e hide.bs.dropdown and show.bs.dropdown).