m/n/core/curator: fix crash in IssueCertificates

Change-Id: Ib0e1f08bfcc2e70cd638f0863450508d10ab9a93
Reviewed-on: https://review.monogon.dev/c/monogon/+/1393
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/core/curator/impl_leader_certificates.go b/metropolis/node/core/curator/impl_leader_certificates.go
index f42b4a4..cb11b99 100644
--- a/metropolis/node/core/curator/impl_leader_certificates.go
+++ b/metropolis/node/core/curator/impl_leader_certificates.go
@@ -27,6 +27,9 @@
 	}
 
 	kubeletServer, kubeletClient, err := kp.Kubelet(ctx, nodeID, req.KubeletPubkey)
+	if err != nil {
+		return nil, status.Errorf(codes.Unavailable, "could not generate kubelet certificates: %v", err)
+	}
 
 	kubeletServerCert, err := kubeletServer.Ensure(ctx, kp.KV)
 	if err != nil {