fix: pass empty string email content of pos invoice

(cherry picked from commit ee7bd98878)

erpnext/selling/page/point_of_sale/pos_past_order_summary.js

@@ -264,6 +264,7 @@ erpnext.PointOfSale.PastOrderSummary = class {
 				content: content ? content : __(frm.meta.name) + ": " + doc.name,
 				doctype: doc.doctype,
 				name: doc.name,
+				content: "",
 				send_email: 1,
 				print_format,
 				sender_full_name: frappe.user.full_name(),