fix: nil pointer in network checker of liqoctl info peer

[claudiolor]

Description

When the Endpoint field of the status of the GatewayServer resource is empty, liqoctl info peer returned a nil pointer exception.
This PR fixes this issue.

[adamjensenbot]

Hi @claudiolor. Thanks for your PR!

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[fra98]

/rebase test=true

[fra98]

/rebase test=true