Nice error when dead nodes are passed to cstar

[Bj0rnen]

From @Yarin78 on July 12, 2018 12:29

When a dead node is passed to cstar, cstar will complain about empty JSON, not about the dead node. Dead nodes are kinda common, they happen when they are taken out of ring, but kept alive, which allows disco to report them, and when such disco gets into cstar, we get a JSON complain.