NFSv4: Validate the stateid before applying it to state recovery

If the stateid is the zero or invalid stateid, then it is pointless
to attempt to use it for recovery. In that case, try to fall back
to using the open state stateid, or just doing a general recovery
of all state on a given inode.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>