[FIX] web: call do_hide/do_show on a destroyed widget

Before this commit, calling do_hide/do_show/do_toggle on a
widget that had been destroyed before being rendered crashed
(because this.$el was undefined).

Obviously, calling those methods in this situation is useless, but
with asynchronous code, it might happen that you call them in an
handler, and they have been destroyed meanwhile.

This commit checks if this.$el is set before accessing it to avoid
the crash.

closes odoo/odoo#65885

X-original-commit: 320c29f5
Signed-off-by: Géry Debongnie (ged) <ged@openerp.com>