Make lntop process terminate when lnd becomes unreachable

[xanoni]

I noticed that lntop just hangs if lnd crashes or otherwise becomes unreachable. Besides, it still keeps hanging and doesn't recover when lnd becomes reachable again after a while.

That makes it difficult to rely on lntop alone for visual status monitoring. I've had a few situations where everything seemed great, but in realitylnd was long dead already and hadn't come back up (e.g., when I was out of disk space ...).

[edouardparis]

Thank you for reporting the issue. It totally agree with the problem. It will take time, but I will look for a fix.