[FIX] mail: no traceback on receiving seen notification

Before this commit, when we post a message and someone
has received it, there could be a traceback.

Steps to reproduce:
1. Two users are logged in.
2. On one user:
   - open any app except Discuss
   - From systray messaging menu, click on "New messages"
   - Open Discuss
   - Post a message in a direct chat with other User.
> traceback `Cannot read property 'getID' of null`

closes odoo/odoo#31228

1 files changed, 3 insertions, 0 deletions

diff --git a/addons/mail/static/src/js/thread_windows/thread_window.js b/addons/mail/static/src/js/thread_windows/thread_window.js
index 331228c91c8..d7f6acbda5f 100644
--- a/addons/mail/static/src/js/thread_windows/thread_window.js
+++ b/addons/mail/static/src/js/thread_windows/thread_window.js
@@ -377,6 +377,9 @@ var ThreadWindow = AbstractThreadWindow.extend({
      * @param {integer} channelID
      */
     _onUpdateChannel: function (channelID) {
+        if (!this.hasThread()) {
+            return;
+        }
         if (this._thread.getID() !== channelID) {
             return;
         }