nfsd4: fix corruption on setting an ACL.

As of 06f9cc12 "nfsd4: don't create
unnecessary mask acl", any non-trivial ACL will be left with an
unitialized entry, and a trivial ACL may write one entry beyond what's
allocated.
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4acl.c

@@ -590,7 +590,7 @@ posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
 		add_to_mask(state, &state->groups->aces[i].perms);
 	}
 
-	if (!state->users->n && !state->groups->n) {
+	if (state->users->n || state->groups->n) {
 		pace++;
 		pace->e_tag = ACL_MASK;
 		low_mode_from_nfs4(state->mask.allow, &pace->e_perm, flags);