--email-obfuscation=none mangles nested tags within mailto links in HTML output

Running `pandoc --email-obfuscation=none -o test.html test.md` on this `test.md` file:

```
[E-mail the *incredible* me](mailto:me@example.net)
```

produces this `test.html` file:

``` html
<a href="mailto:me@example.net">E-mail the &lt;em&gt;incredible&lt;/em&gt; me</a>
```

instead of the expected:

``` html
<a href="mailto:me@example.net">E-mail the incredible me</a>
```