[markdown] Multi-line blockquotes break nested single-line blockquotes

> First paragraph
>
> Second paragraph
>
> Third paragraph

First paragraph

Second paragraph

Third paragraph

1

---

>>> First paragraph
>>>
>>> Second paragraph
>>>
>>> Third paragraph

First paragraph

Second paragraph

Third paragraph

2

---

> foo
>> bar
>>
>> baz

> boo
>> far
>>
>> faz

foo

bar

baz

boo

far

faz

3

---

> foo
>>> bar
>>>
>>> baz

> boo
>>> far
>>>
>>> faz

foo

bar

baz

boo

far

faz

4