Many of the newer stock vending machines (see photo) have a "double-door lock" mechanism in their dispensary. Postboxes and book returns also employ this mechanism.
The principle of the device is to keep the inside of the vending machine completely sealed and inaccessible at all times. Reaching into the machine through the frontal door (lock) automatically forces the more distal door shut, which (for example) prevents a piece of wire from being forced up inside the machine to pilfer the goodies.
Is there a recognized name for this type of double-door lock mechanism?
Web searches for "vending machine locks", "vending machine doors", "vending machine dispensing devices", etc. have proven fruitless due to the fact that "vending machine" refers to a remarkably broad range of devices, all of which have a variety of locks, doors, latches, and dispensary mechanisms.