net/dns: resolveConfExists reading the wrong error

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

net/dns/direct.go

@@ -216,7 +216,8 @@ func (m directManager) restoreBackup() error {
 	if err != nil {
 		return err
 	}
-	if _, err := m.fs.Stat(resolvConf); err != nil && !os.IsNotExist(err) {
+	_, err = m.fs.Stat(resolvConf)
+	if err != nil && !os.IsNotExist(err) {
 		return err
 	}
 	resolvConfExists := !os.IsNotExist(err)