[fix] POS not working if user clicks on back button from form view (#10912)

diff --git a/erpnext/selling/page/point_of_sale/point_of_sale.js b/erpnext/selling/page/point_of_sale/point_of_sale.js
index d4b7eba..ec1a292 100644
--- a/erpnext/selling/page/point_of_sale/point_of_sale.js
+++ b/erpnext/selling/page/point_of_sale/point_of_sale.js
@@ -20,6 +20,10 @@
 	});
 };
 
+frappe.pages['point-of-sale'].refresh = function(wrapper) {
+	cur_frm = wrapper.pos.frm;
+}
+
 erpnext.pos.PointOfSale = class PointOfSale {
 	constructor(wrapper) {
 		this.wrapper = $(wrapper).find('.layout-main-section');
@@ -478,6 +482,8 @@
 	}
 
 	update_taxes_and_totals() {
+		if (!this.frm.doc.taxes) { return; }
+
 		const currency = this.frm.doc.currency;
 		this.frm.refresh_field('taxes');