Handle URLs more robustly

[mingjun97]

• code-server version: docker default version
• OS Version: docker CE inside Debian

Steps to Reproduce

1. Establish reverse proxy via nginx with mapping https://xxxx/ide/ to http://localhost:8443/
2. The page showed GET // Failed.

I also tried other configurations. But this configuration seems to be the most correct. I guess the URL handler should be more robust to handle URLs like this.

[NGTmeaty]

Open PR #149