webdav: fix dropped test error

Picks up a dropped error in TestMemLSConfirm().

Change-Id: Idfbb0fc37dcbec55b0ec6343221dcd9310f474b8
Reviewed-on: https://go-review.googlesource.com/c/net/+/206218
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

webdav/lock_test.go

@@ -212,6 +212,10 @@ func TestMemLSConfirm(t *testing.T) {
 		Duration:  infiniteTimeout,
 		ZeroDepth: false,
 	})
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+
 	tweedle, err := m.Create(now, LockDetails{
 		Root:      "/tweedle",
 		Duration:  infiniteTimeout,