Windows: fix cm_DirOpDelBuffer assert

Windows: fix cm_DirOpDelBuffer assert

In cm_DirOpDelBuffer() the data version field for a buffer
in cm_dirOp_t.buffers[] can be CM_BUF_VERSION_BAD if the buffer
was added to the buffer list but was never fetched from the file
server.  If the buffer was recycled by buf_Get() an attempt to
remove an entry from the directory will be failed as opposed to
fetching the buffer from the file server and performing the local
removal.

Reviewed-on: http://gerrit.openafs.org/6650
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 865f2442e682ff71b28a6b21363de8262f9e2bd1)

Change-Id: I4d822d9286ca891fc50cf04fdd68272c0af2e38e
Reviewed-on: http://gerrit.openafs.org/6828
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>