OpenBSD apparently doesn't allow unmapping address space if part of the region is already unmapped.
This tweaks the test so that munmapping twice no longer happens.
Fixesgolang/go#68181
Change-Id: I588255f5e10ec015dbb7188eac79cee6be570680
GitHub-Last-Rev: 2535abd892d9063b9bdda69101a45f71c4174124
GitHub-Pull-Request: golang/sys#199
Cq-Include-Trybots: luci.golang.try:go1.22-openbsd-amd64
Reviewed-on: https://go-review.googlesource.com/c/sys/+/595095
TryBot-Bypass: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>