Using double forward slash in URL returns HTML instead of performing an API request #9877
Description
The issue can be demonstrated easily:
~
❯ curl https://dev.coder.com/api/v2/buildinfo
{"external_url":"https://github.com/coder/coder/commit/6f0e2a79683d30c2974fbe9cda5802f0b7c47d44","version":"v2.1.5-devel+6f0e2a796","dashboard_url":"https://dev.coder.com","workspace_proxy":false}
vs
~
❯ curl https://dev.coder.com//api/v2/buildinfo
<!doctype html>
<!--
▄█▀ ▀█▄
▄▄ ▀▀▀ █▌ ██▀▀█▄ ▐█
▄▄██▀▀█▄▄▄ ██ ██ █▀▀█ ▐█▀▀██ ▄█▀▀█ █▀▀
█▌ ▄▌ ▐█ █▌ ▀█▄▄▄█▌ █ █ ▐█ ██ ██▀▀ █
██████▀▄█ ▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀ ▀▀▀▀ ▀
-->
<head>
This could probably be considered a non-bug, but I'm reporting it as a bug. It's not an uncommon scenario when concatenating URLs (ran into this in #9852) that we could handle. Perhaps we can sanitize all (or at least most) // to /?