Fix cart redirect after crypto payment cancellation

Use simple /cart route which automatically goes to active cart instead of
trying to construct specific cart checkout URL with non-existent cart_id field.

make_post_sell/views/crypto.py

@@ -733,9 +733,7 @@ def crypto_cancel(request):
     request.dbsession.flush()
 
     # Get the cart URL for redirect
-    cart_url = request.route_url(
-        "user_cart_checkout", cart_id=crypto_payment.invoice.cart_id
-    )
+    cart_url = request.route_url("cart")
 
     return Response(
         json.dumps(