Fixes panic error when TLSEnabled flag is not set

[jjaferson]

Closes: #39

#Verification Steps

1. install the operator
2. create an instance of authorino with the spec below

 kubectl create namespace myapi 

kubectl -n myapi apply -f -<<EOF
apiVersion: operator.authorino.kuadrant.io/v1beta1
kind: Authorino
metadata:
  name: authorino
spec:
  replicas: 1
  clusterWide: false
  listener:
    tls:
      certSecretRef:
        name: authorino-server-cert
  oidcServer:
    tls:
      certSecretRef:
        name: authorino-oidc-server-cert
EOF

3. Check if the status block of the authorino CR is showing an error

 kubectl get authorino authorino -n myapi -o yaml

 ...
 status:
  conditions:
  - lastTransitionTime: "2022-04-28T15:12:21Z"
    message: 'listener secret name authorino-server-cert not found, err: Secret "authorino-server-cert"
      not found'
    reason: TlsSecretNotProvided
    status: "False"
    type: Ready