nmcli: always clean up readline on exit
A signal handler is not the only place where we need to clean up after an in-progress readline() on exit; we may do so when erroring out as well:
Before (not also the missing line break, which is part of the cleanup):
$ (sleep 10; nmcli c del 'Red Hat Wi-Fi')
$ nmcli --ask d wifi connect 'Red Hat Wi-Fi'
Passwords or encryption keys are required to access the wireless network 'Red Hat Wi-Fi'.
Password (802-11-wireless-security.psk): Error: Connection activation failed: The device's active connection disappeared.
$ [terminal messed up, no echo]
After:
$ (sleep 10; nmcli c del 'Red Hat Wi-Fi')
$ nmcli --ask d wifi connect 'Red Hat Wi-Fi'
Passwords or encryption keys are required to access the wireless network 'Red Hat Wi-Fi'.
Password (802-11-wireless-security.psk):
Error: Connection activation failed: The device's active connection disappeared.
$ hello [terminal echo fine, wheee]