[accounts.reddit.com] Redirect parameter allows for XSS

## Summary: Hello team! I was tampering with the dest parameter in accounts.reddit.com and found out it is vulnerable to Cross Site Scripting once the victim performs the log in. ## Steps To Reproduce: 1. Enter to the following link: ```https://accounts.reddit.com/?dest=blocked:alert(document.domain)``` - If not signed in, the user will be promped to log in and after doing so XSS will excecute {F2315850} - If user is logged into his account, following the link will also make the XSS pop up {F2315847} ## Impact An attacker could trick users into executing XSS, executing code and stealing their cookies only by them logging in.