[FIX] web_editor: do not traceback on null selection

Because the `selectionchange` event is async, the selection can
be null if the node has been removed between the moment the
selection was moved and the moment the event is triggered.

X-original-commit: 3232edb1ccb196c992f75858fe81d08a5af58ab9
Part-of: odoo/odoo#113540

addons/web_editor/static/src/js/editor/odoo-editor/src/OdooEditor.js

@@ -3580,6 +3580,12 @@ export class OdooEditor extends EventTarget {
      */
     _onSelectionChange() {
         const selection = this.document.getSelection();
+        if (!selection) {
+            // Because the `selectionchange` event is async, the selection can
+            // be null if the node has been removed between the moment the
+            // selection was moved and the moment the event is triggered.
+            return;
+        }
         const anchorNode = selection.anchorNode;
         if (anchorNode && closestElement(anchorNode, '[data-oe-protected="true"]')) {
             return;