Regression: a list is broken if an item starts with a fenced code block

Input:
```markdown
-   ```
    foo
    ```

-   bar
```

Expected output (the first item has `<pre>`):
```html
<ul>
<li><pre><code>foo
</code></pre></li>

<li><p>bar</p></li>
</ul>
```

New output since f1f45ab (the first item lacks `<pre>`; the second item is not recognized as an item):
```html
<ul>
<li><code>
foo
</code>

-   bar</li>
</ul>
```
