[FIX] point_of_sale: Prevent traceback if opening cash is empty

A TypeError traceback that occurs in `set_cashbox_pos`
was caught by Sentry.

If the user validates the openingCash with an empty input, the
clientside code sends an empty string instead of a number to the python
code which interprets it as a number.

https://github.com/odoo/odoo/blob/84347b43063fc3032da3e03b49fc57375d8324fc/addons/point_of_sale/models/pos_session.py#L1480-L1485

opw-3089337

closes odoo/odoo#107303

X-original-commit: 62f0117c0f5fad1cd435c65986d477432de00dfa
Signed-off-by: Achraf <abz@odoo.com>

addons/point_of_sale/static/src/js/Popups/CashOpeningPopup.js

@@ -43,6 +43,10 @@ odoo.define('point_of_sale.CashOpeningPopup', function(require) {
         handleInputChange() {
             this.manualInputCashCount = true;
             this.moneyDetails = null;
+            this.state.notes = "";
+            if (typeof(this.state.openingCash) !== "number") {
+                this.state.openingCash = 0;
+            }
         }
     }