cmd/go: do not ignore permission errors when matching patterns
While reviewing CL 228784, I noticed that various filepath.WalkFunc
implementations within cmd/go were dropping non-nil errors.
Those errors turn out to be significant, at least in some cases: for
example, they can cause packages to appear to be missing when any
parent of the directory had the wrong permissions set.
(This also turned up a bug in the existing list_dedup_packages test,
which was accidentally passing a nonexistent directory instead of the
intended duplicate path.)
Change-Id: Ia09a0a33aa7a966d9f132d3747d6c674a5370b2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/232579
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Jay Conrod <jayconrod@google.com>