try to fix #997 ,when cart is disabled, it will not show error and it will dedirect to 'contact' page (#8636)

diff --git a/erpnext/shopping_cart/cart.py b/erpnext/shopping_cart/cart.py
index 61ec78c..66e9f4c 100644
--- a/erpnext/shopping_cart/cart.py
+++ b/erpnext/shopping_cart/cart.py
@@ -315,7 +315,8 @@
 
 	else:
 		if not cart_settings.enabled:
-			return None
+			frappe.local.flags.redirect_location = "/contact"
+			raise frappe.Redirect
 		customer = frappe.new_doc("Customer")
 		fullname = get_fullname(user)
 		customer.update({