fix ISTIO config checking error

(cherry picked from commit de7f6da2)

devops/azure/chart/templates/virtual-service.yaml

 ---
 # Source: /devops/azure/chart/templates/virtual-service.yaml
+{{- if .Values.istioDnsHost }}
 apiVersion: networking.istio.io/v1alpha3
 kind: VirtualService
 metadata:
@@ -32,4 +33,5 @@ spec:
       - PATCH
       - DELETE
       allowOrigins:
-      - prefix: "*"
\ No newline at end of file
+      - prefix: "*"
+{{- end }}
\ No newline at end of file