[FIX] point_of_sale: fix hitting backspace on 0 quantity line

Fine tuning of 02d9b51e

Steps:
- Install l10n_fr_pos_cert
- Open POS session with French company
- Add product
- Hit backspace: set new quantity to 0
- Hit backspace again

Error will be shown. This occur because `event.detail.buffer` might be null

closes odoo/odoo#74711

Signed-off-by: agr-odoo <agr-odoo@users.noreply.github.com>

addons/point_of_sale/static/src/js/Screens/ProductScreen/ProductScreen.js

@@ -171,7 +171,7 @@ odoo.define('point_of_sale.ProductScreen', function(require) {
                     });
                     return;
                 }
-                const parsedInput = parse.float(event.detail.buffer) || 0
+                const parsedInput = event.detail.buffer && parse.float(event.detail.buffer) || 0;
                 if(lastId != selectedLine.cid)
                     this._showDecreaseQuantityPopup();
                 else if(currentQuantity < parsedInput)