net: prevent unintended retries upon receiving an empty answer response from the DNS server.
CL https://golang.org/cl/37879 migrates DNS message parsing to the golang.org/x/net/dns/dnsmessage package. However, during the modification of the "lame referral" error check introduced by CL https://golang.org/cl/22428, a condition was overlooked. This omission results in unexpected retries when a DNS server returns an empty response (not an invalid response, but one that includes an additional section).
Fixes #57697
Fixes #64783
Change-Id: I203896aa2902c305569005c1712fd2f9f13a9b6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/550435
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Damien Neil <dneil@google.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Dexter Ouyang <kkhaike@gmail.com>