Fix potential crash on network check (DEV) (#3066)

```
java.lang.IllegalArgumentException:
  at com.android.internal.util.Preconditions.checkArgument (Preconditions.java:52)
  at android.net.ConnectivityManager.unregisterNetworkCallback (ConnectivityManager.java:4750)
  at de.rki.coronawarnapp.util.network.NetworkStateProvider$networkState$1$2.invoke (NetworkStateProvider.kt:4)
```

Co-authored-by: harambasicluka <64483219+harambasicluka@users.noreply.github.com>