get rid of check_path(), it's overly complicated. Instead, inline open_file() in client_read() and rework open_dir() to just use openat() instead of the complicate dance it was doing. Simplify open_dir() too in the process: if the directory entry for the index is not a regular file, pretend it doesn't exist.

in those cases we need to reschedule the function and return, instead of going on with the cleanup.

If a TLS handshake fails there's nothing we can do, so don't attempt to reply an error (the connected client is not speaking Gemini as it's not using TLS at all) and instead just close the connection. Fixes issue #13