.lines returns string "0" for blank lines

A minimal case which runs on the latest master.

```
var Lazy = require('./lazy');
var l = new Lazy();
l.lines.forEach(function (x) { console.log(x); });
l.emit('data', 'abc\n\n');
```

Actual output:

```
<Buffer 61 62 63>
<Buffer 30>
```

Expected output:

```
<Buffer 61 62 63>
<Buffer >
```
