reorder presence detection write headers to remove warnings

[zackattack01]

noticed these logs while debugging:

"msg":"2025/01/03 10:24:42 http: superfluous response.WriteHeader call from github.com/kolide/launcher/ee/desktop/user/server.(*UserServer).detectPresence (server.go:234)","component":"desktop_runner"

reading the docs this happens when WriteHeader is called multiple times, or after Write is called. this is harmless in our current invocation because http package will write a default OK status, but ordering these correctly should remove the warnings