Due to err being shadowed in the else brach, the actual err return of
fd1.Chdir() is never checked. Fix it by not shadowing err anymore.

Change-Id: I9f1d52e88d8bc9a1c035960aa7af9f5224a63ab0
Reviewed-on: https://go-review.googlesource.com/80556
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>