Not calling call.respond() at server results in 404 for the client

Calling a service from the client results in a 404-error if the server does not respond with a
```call.respond()```
404 Not Found is a bit missleading here.

ktorVersion = "1.0.0-beta-3"
Discussion at Slack: https://kotlinlang.slack.com/archives/C0A974TJ9/p1542617591326600

Start by tracing server-side request handling when a service omits call.respond(), as described in the issue; no source files or tests are identified. Review the Slack discussion for the intended behavior, then define a regression test that captures the expected client-visible result instead of the current 404.

Written by the indexing model from the issue text.