Status endpoint fails if there are no blocks

[kostko]

Currently the status endpoint (GetStatus) will fail if the node doesn't yet have any blocks because it tries to load the validator set and fails with:

{“caller”:“grpc.go:202”,“err”:“failed to get consensus status: failed to load validator set: could not find validator set for height #1”,“level”:“error”,“method”:“/oasis-core.NodeController/GetStatus”,“module”:“grpc/internal”,“msg”:“request failed”,“req_seq”:117,“ts”:“2020-11-04T13:52:24.340094029Z”}

This may be related to starting with a height greater than 1.