Only set stream status zone if hostname exists

[sjberman]

Problem: Noticed during conformance tests, the stream server blocks did not have a hostname, and therefore the status_zone value was empty and invalid.

Solution: Only set the status_zone directive if it has a value.

Closes #2683

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

Stream status_zone directive is no longer set if its value is empty.