exit command requires an extra <enter>

in MAVProxy, when I type "exit", then press enter, MAVproxy doesn't exit. But if I hit enter again, it does.


Start by reproducing the issue in MAVProxy: type `exit` and press Enter once, then inspect the command and input-handling entry points responsible for processing that input. Done means the command exits on the first Enter press, with a regression check if the existing test structure provides one.

Written by the indexing model from the issue text.