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.

Change-Id: Id9af5180f2176c2a90ef9907ae84139e66ffe5d6
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>