Fix potential nil pointer panic in check-gke-ingress

[ruixiansong]

/assign @swetharepakula

[k8s-ci-robot]

Hi @songrx1997. Thanks for your PR.

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[swetharepakula]

/ok-to-test

[swetharepakula]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: songrx1997, swetharepakula

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