Infinite loop when parsing multiline blockquotes with non-prefixed lines

Hey!

The following documents cause an infinite loop while parsing:

```jot
> wibble
wobble
woo
```

```jot
> wibble
wobble
> woo
```

```jot
> wibble
wobble

woo
```

A single line continuation (`> wibble\nwobble`) works.

It's really cool a far this library has come, I replaced all my markdown with djot, thank you!

~ 💜 
