Theme change redirect URL always takes user to SO (because missing SE subdomain string)

[opusforlife2]

What's Happening?

Clicking/tapping on the theme toggle button takes the user to that question number (if it exists) on SO, instead of whatever SE subdomain they were on.

How to reproduce:

1. Open https://overflow.projectsegfau.lt/exchange/scifi/questions/218381/how-does-a-horcrux-work
2. Click/tap on theme toggle.
3. See that you're taken to an SO question with the corresponding URL: https://overflow.projectsegfau.lt/options/theme?redirect_url=https%3a%2f%2foverflow.projectsegfau.lt%2fquestions%2f218381%2fhow-does-a-horcrux-work

Affected Platforms:

• All

Version: 1.10.1

Browser:

• Chromium-based (ex: Brave or Chrome)
• Webkit-based (ex: Safari)
• Gecko-based (ex: Firefox)