multipipe(readable, multipipe(transform, writable, cb1), cb2) fails

This code works:
```
multipipe(readable, transform, writable, cb)
```

This code does not work:
```
multipipe(readable, multipipe(transform, writable, cb1), cb2)
```

Reason: `multipipe(transform, writable, cb1)` returns a transform stream, not a writable stream