NFSv4: Ensure asynchronous open() calls always pin the mountpoint

A number of race conditions may currently ensue if the user presses ^C
and then unmounts the partition while an asynchronous open() is in
progress.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index c27258b..4948ec1 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1244,7 +1244,7 @@
 	attr.ia_mode = mode;
 	attr.ia_valid = ATTR_MODE;
 
-	if (nd && (nd->flags & LOOKUP_CREATE))
+	if ((nd->flags & LOOKUP_CREATE) != 0)
 		open_flags = nd->intent.open.flags;
 
 	lock_kernel();