Fix statusCode 0 write panic

[malud]

This pull request should fix two rare cases which would lead to possible statusCode 0 writes to the client. A panic thrown by the http package will prevent this. One way could be to read an invalid gzip header and processing further with already read body bytes (gzipheader, 10bytes) which could also lead to content-length != body.len write errors.

a) handle gzip reader creation error, reset backend response body
b) add a fallback to our responseWriter to write at least status 500

---

Reviewer checklist

• Read PR description: a summary about the changes is required
• Changelog updated
• Documentation: docs/{Reference, Cli, ...}, Docker and cli help/usage
• Pulled branch, manually tested
• Verified requirements are met
• Reviewed the code
• Reviewed the related tests