Unindented code blocks with tags causes wrong output

[gptt916]

When tagging something with the pre tag that is nested in lists, unindented items causes an error in output, even though they are technically valid markdown.

Wrong output (see double pre classname):

input:

{:pre: .pre}

- item:
```
code
```
{:pre}

- item 1:
```
code
```
{:pre}

output:

<ul clas='pre pre'>
  <li>
    <p>item</p>
    <pre class="pre"><code class="hljs">code</code></pre>
  </li>
  <li>
    <p>item 1</p>
    <pre class="pre"><code class="hljs">code</code></pre>
  </li>
</ul>

---

correct output:

{:pre: .pre}

- item:
    ```
    code
    ```
    {:pre}

- item 1:
    ```
    code
    ```
    {:pre}

<ul >
  <li>
    <p>item</p>
    <pre class="pre"><code class="hljs">code</code></pre>
  </li>
  <li>
    <p>item 1</p>
    <pre class="pre"><code class="hljs">code</code></pre>
  </li>
</ul>