As fullwings pointed out, Boeing designed the AT not to autowake-up in FLCH mode.
However, the AP (if in CMD) or the flight control system (if manual flight) provide independent envelope protection.
If in CMD, the AP will prevent the aircraft from going below min maneuver speed, so it will transition to a descent, and you will get an AUTOPILOT caution message.
If manual flight, the aircraft will not trim below min maneuver speed. The pilot would have to apply continuous column force to go below min speed, with higher force than that required for an equivalent out-of-trim condition above min speed.
So in manual flight, you could stall it but you would have to really mean to.
