export_connection_profile() crashed the whole installer under set -e/
pipefail when the active NetworkManager connection has no backing
keyfile (common for ephemeral live-boot DHCP connections) - nmcli
returned a non-zero exit status even though the guard below already
handles an empty result gracefully. Every other nmcli call in this
function already has this || true safety net; this one was missing it.
Found via a live end-to-end boot test in Proxmox.
