Links to headers in markdowns fail to load

Headers in markdowns open a webview with the following error:
“Safari cannot open the page. The error was the URL can’t be shown”

[Link to video of the problem](https://twitter.com/marcterns/status/1049800514907623424?s=12)

<details>
<summary>Bug Report Dump (Auto-generated)</summary>
<pre>
Version 1.23.0 (1537716040)
Device: iPhone X (iOS 12.0)
TestFlight: true
</pre>
</details>