Request prompt doesn't show if you generate an error while editing the cart

[orenyk]

Steps to replicate:

1. Add item to cart with valid reservation parameters
2. Click "Reserve" while viewing as Patron
3. Change reservation parameters to violate a validation (e.g. increase beyond availability)

Expected: View switches to request form with prompt from app configs
Actual: View switches to request form but prompt is empty

I'll get this fixed ASAP.