PeerStatus.AllowedIPs is only populated when a peer has allowed IPs, so
it is nil for peers whose backing nodes are offline or not yet approved,
such as a kube-apiserver ProxyGroup with no healthy nodes. When the
argument to "tailscale configure kubeconfig" resolved to a Tailscale
Service ExtraRecord, nodeOrServiceDNSNameFromArg iterated AllowedIPs of
every peer without a nil check and panicked with SIGSEGV.
Skip peers with no AllowedIPs so the command reports the existing "is in
MagicDNS, but is not currently reachable on any known peer" error
instead of crashing.
Fixes#20255
Signed-off-by: Salih Muhammed <root@lr0.org>
9106b237eb