cmping hangs if cached configured account cannot connect

[link2xt]

To reproduce:

1. Configure an account on some server by running cmping example.org example.org (I used ci-chatmail.testrun.org)
2. Configure nftables to drop all packets
3. Run cmping again, see it hangs forever on "waiting for profiles to be online":

Hangs in this loop:

cmping/cmping.py

Lines 414 to 417 in 7f69237

	while any(t.is_alive() for t in threads):
	print_progress("Waiting for profiles to be online", spinner_idx=spinner_idx)
	spinner_idx += 1
	time.sleep(0.1)