[FIX] mail: prevent from closing an already deleted chat window

task-2394789

closes odoo/odoo#62626

X-original-commit: c32a3e9cbe0323e0b1fcc70b1438e9a56185493c
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/components/chat_window_header/chat_window_header.js

@@ -100,6 +100,9 @@ class ChatWindowHeader extends Component {
      */
     _onClickClose(ev) {
         ev.stopPropagation();
+        if (!this.chatWindow) {
+            return;
+        }
         this.chatWindow.close();
     }