Fix crash due to missing ingress http block

It's acceptable although uncommon for an ingress to have a rule and a host,
but no HTTP block for that particular rule.

internal/store/ingress.go

@@ -104,10 +104,18 @@ var (
 			GenerateFunc: wrapIngressFunc(func(i *v1beta1.Ingress) *metric.Family {
 				ms := []*metric.Metric{}
 				for _, rule := range i.Spec.Rules {
-					for _, path := range rule.HTTP.Paths {
+					if rule.HTTP != nil {
+						for _, path := range rule.HTTP.Paths {
+							ms = append(ms, &metric.Metric{
+								LabelKeys:   []string{"host", "path", "service_name", "service_port"},
+								LabelValues: []string{rule.Host, path.Path, path.Backend.ServiceName, path.Backend.ServicePort.String()},
+								Value:       1,
+							})
+						}
+					} else {
 						ms = append(ms, &metric.Metric{
 							LabelKeys:   []string{"host", "path", "service_name", "service_port"},
-							LabelValues: []string{rule.Host, path.Path, path.Backend.ServiceName, path.Backend.ServicePort.String()},
+							LabelValues: []string{rule.Host, "", "", ""},
 							Value:       1,
 						})
 					}

internal/store/ingress_test.go

@@ -139,6 +139,9 @@ func TestIngressStore(t *testing.T) {
 								},
 							},
 						},
+						{
+							Host: "somehost2",
+						},
 					},
 				},
 			},
@@ -148,6 +151,7 @@ func TestIngressStore(t *testing.T) {
 				kube_ingress_metadata_resource_version{namespace="ns4",resource_version="abcdef",ingress="ingress4"} 1
 				kube_ingress_labels{label_test_4="test-4",namespace="ns4",ingress="ingress4"} 1
 				kube_ingress_path{namespace="ns4",ingress="ingress4",host="somehost",path="/somepath",service_name="someservice",service_port="1234"} 1
+				kube_ingress_path{namespace="ns4",ingress="ingress4",host="somehost2",path="",service_name="",service_port=""} 1
 				kube_ingress_annotations{namespace="ns4",ingress="ingress4",annotation_test_4="test-4"} 1
 `,
 			MetricNames: []string{"kube_ingress_info", "kube_ingress_metadata_resource_version", "kube_ingress_created", "kube_ingress_labels", "kube_ingress_path", "kube_ingress_annotations"},