Fix panic in GCE loadbalancer library

pkg/cloudprovider/providers/gce/gce_loadbalancer_external.go

@@ -344,7 +344,10 @@ func (gce *GCECloud) ensureExternalLoadBalancerDeleted(clusterName, clusterID st
 			glog.Infof("ensureExternalLoadBalancerDeleted(%s): Failed to retrieve health check:%v.", lbRefStr, err)
 			return err
 		}
-		hcNames = append(hcNames, hcToDelete.Name)
+		// If we got 'StatusNotFound' LB was already deleted and it's safe to ignore.
+		if err == nil {
+			hcNames = append(hcNames, hcToDelete.Name)
+		}
 	} else {
 		// EnsureLoadBalancerDeleted() could be triggered by changing service from
 		// LoadBalancer type to others. In this case we have no idea whether it was