[fixes #83598468] fix crash if config has env: thats undefined

sample config:

```javascript
{
  "mySection": {
    "appDefault": "env:I_EXPECT_NOTHING_HERE_APP",
    "appEnv": "env:I_EXPECT_NOTHING_HERE_APP_ENV"
  }
}
```
If the environment variables were not set, starting
koast would simply crash instead of displaying config
debug info