client: fix erroneous error message in dupOrRename
client: fix erroneous error message in dupOrRename

Change-Id: I187645bdfe7fb54d6b8dc81cb506ce7af55144a2
Reviewed-on: https://upspin-review.googlesource.com/12540
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin