add nil check when reading endpoint hostname

[adleong]

Fixes #12686

When an endpoint in an EndpointSlice resource does not contain a hostname field, the destination controller can panic while looking for an endpoint with a certain hostname. This happens when doing a lookup with a pod dns name.

We add a nil check to avoid the panic.

We add such an endpoint to our test fixture to exercise this case.

[acallejaszu]

Thanks for the quick response on this! It would be nice to see a mention as this is the fix I proposed in the issue, but :man-shrugging:

[adleong]

@acallejaszu Yes, absolutely! Thank you so much for finding, root causing, and solving this bug. I do want to make sure that you're properly credited. What did you have in mind?

[acallejaszu]

Hey @adleong thanks for your response! Just a mention in the release description/changelog where you will include this bug fix will be more than enough. Thanks!