lib9: null d->ext during nulldir

src/lib9/nulldir.c

diff --git a/src/lib9/nulldir.c b/src/lib9/nulldir.c
index 612725d..302b996 100644
--- a/src/lib9/nulldir.c
+++ b/src/lib9/nulldir.c
@@ -5,5 +5,5 @@
 nulldir(Dir *d)
 {
 	memset(d, ~0, sizeof(Dir));
-	d->name = d->uid = d->gid = d->muid = "";
+	d->name = d->uid = d->gid = d->muid = d->ext = "";
 }