fix: do not create ingressclass when it's empty (alibaba#1419)

Signed-off-by: fengxusong <[email protected]>

Author: fengxsong

Diff for: helm/core/templates/ingressclass.yaml

@@ -1,6 +1,8 @@
+{{- if .Values.global.ingressClass }}
 apiVersion: networking.k8s.io/v1
 kind: IngressClass
 metadata:
   name: {{ .Values.global.ingressClass }}
 spec:
-  controller: higress.io/higress-controller
+  controller: higress.io/higress-controller
+{{- end }}