enhancement: do nothing if cancel_sbscription is called for cancelled subscription

erpnext/accounts/doctype/subscriptions/subscriptions.py

@@ -396,6 +396,7 @@ class Subscriptions(Document):
 		This sets the subscription as cancelled. It will stop invoices from being generated
 		but it will not affect already created invoices.
 		"""
+		if self.status != 'Canceled':
 			to_generate_invoice = True if self.status == 'Active' else False
 			to_prorate = frappe.db.get_single_value('Subscription Settings', 'prorate')
 			self.status = 'Canceled'