quorum: Make bdrv_dirname() return NULL
While the common implementation for bdrv_dirname() should return NULL
for quorum BDSs already (because they do not have a file node and their
exact_filename field should be empty), there is no reason not to make
that explicit.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id:
20190201192935.18394-17-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>