Previously, only one popup is allowed such that when one is not
yet close, but another one is requested, the new one will replace
the old. The function that tries to wait for the replaced popup
will never resolve resulting to some potential broken state.
This commit resolves the said issue which now allows multiple
popups at a time. We can use POS instance without demo as an
example.
Before this commit: The popup that asks whether to load the demo
products will be shown but it will be replaced by the cash opening
popup.
After this commit: The popup that asks whether to load the demo
products will be shown, then the cash opening popup will show.
When the user is done with the cash opening popup, the demo products
confirmation is shown next.
closesodoo/odoo#83661
Related: odoo/enterprise#23859
Signed-off-by: Masereel Pierre <pim@odoo.com>