cmd/upspinfs: fix an infinite loop in upspinfs after the last close in a directory
cmd/upspinfs: fix an infinite loop in upspinfs after the last close in a directory

Change-Id: If1ee216f09f0eb795c5a48b0aefd8c7c00a4b08e
Reviewed-on: https://upspin-review.googlesource.com/18160
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin