lack of escaping of certain values produces invalid XML

```
$ sf3convert -z -x /usr/share/sounds/sf2/MuseScore_General_Full.sf2 /tmp/x >/dev/null 2>&1
$ xmlstarlet val -e /tmp/x
/tmp/x:2322.23: xmlParseEntityRef: no name
  <Preset name="Bass & Lead" preset="87" bank="0">
                      ^
/tmp/x - invalid
```