syscall: fix closing of reordered FDs in plan9 ForkExec
After dup'ing file descriptors in syscall.ProcAttr.Files to pass
to the exec'ed process, the logic for closing the old descriptors
was incorrect and could close the new descriptor instead.
Fixes #57180
Change-Id: I7725f21a465ffba57050fe4e36f3d36ba181cfb2
Reviewed-on: https://go-review.googlesource.com/c/go/+/457115
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: David du Colombier <0intro@gmail.com> Reviewed-by: Bryan Mills <bcmills@google.com>