netty: Gzip encoding seems to break AssetHandler

When I enable gzip by adding:
```kotlin
  serverOptions {
    gzip = true
  }
```

My custom html routes returning html are successfully encoded and decoded by the browser, but any assets fail to decode (example from Chrome console):
```
GET http://localhost:8080/build/main.js net::ERR_CONTENT_DECODING_FAILED 200 (OK)
```
