[FIX] web_editor: add check before updateLeftPanel timeout

Added a check to make sure that we do not set a timeout to update the
option panel when said option panel is already open.
This could sometimes occur which could cause all openned select to close
and could fail some tests if said events happened in the middle of
selecting an option.

task-2502297

closes odoo/odoo#69119

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>