HTTP HEAD request returns response body where it should not

[andrew-jones]

Describe the bug
Sending an http head request to ttyd returns the full response body where it should just calculate content-length and return an empty body.

To Reproduce
Steps to reproduce the behavior:

1. Connect to ttyd with telnet - telnet localhost 7681
2. Send HEAD /
3. Hit Enter twice
4. Observe the response body

Expected behavior
Expecting content-length to be set correctly and no data in the response body.

Additional context
This was discovered using a reverse proxy. Caddy (written in golang) logs an error returning a HEAD request from ttyd.

Unsolicited response received on idle HTTP channel starting with \

I use curl --head in my readiness check and the current logging is too verbose and returns the body. So I've dropped --head for now, as the network traffic is the same and I don't want the ttyd index page logged every 20 seconds.