fix: misleading "success" message for DN when SO doesn't exist

Prevent the creation of Delivery Note if Sales Order is missing in ERPN.
Currently the Delivery Note gets created (when order is marked as fulfilled in Shopify) even if the Sales Order against which the DN is to be created is missing in ERPNext.

ecommerce_integrations/shopify/fulfillment.py

@@ -23,7 +23,9 @@ def prepare_delivery_note(payload, request_id=None):
 		sales_order = get_sales_order(cstr(order["id"]))
 		if sales_order:
 			create_delivery_note(order, setting, sales_order)
-		create_shopify_log(status="Success")
+			create_shopify_log(status="Success")
+		else:
+			create_shopify_log(status="Invalid", message="Sales Order not found for syncing delivery note.")
 	except Exception as e:
 		create_shopify_log(status="Error", exception=e, rollback=True)