check cert/key not empty when applying tls setting. (#7610)
check cert/key not empty when applying tls setting. (#7610)

* check cert/key not empty when applying tls setting.

* address comment

smawson/istio,smawson/istio,geeknoid/istio,geeknoid/istio,istio/istio,smawson/istio,istio/istio,geeknoid/istio,istio/istio,istio/istio,smawson/istio,geeknoid/istio,istio/istio,smawson/istio,geeknoid/istio,geeknoid/istio,smawson/istio