[FIX] web_editor: link from the web editor

Before this commit, the feature for selecting a link and then clicking
on the "link" button or hitting the CTRL+K was partially broken.

The method "commonAncestor" was not returing the expected value.

This commit add a check in the method "showLinkDialog" to prevent
this error to happen.

closes odoo/odoo#38103

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/editor/rte.summernote.js

@@ -452,8 +452,11 @@ eventHandler.modules.linkDialog.showLinkDialog = function ($editable, $dialog, l
     $editable.data('range').select();
     $editable.data('NoteHistory').recordUndo();
 
-    var link = linkInfo.range.commonAncestor().closest('a');
-    linkInfo.className = link && link.className;
+    var commonAncestor = linkInfo.range.commonAncestor();
+    if (commonAncestor && commonAncestor.closest) {
+        var link = commonAncestor.closest('a');
+        linkInfo.className = link && link.className;
+    }
 
     var def = new $.Deferred();
     core.bus.trigger('link_dialog_demand', {