Avoid setState on unmounted components

So, I'm using react-resolver with react-router for permissions. So, if a user doesn't pass a certain requirement, they're redirected somewhere. This means that I don't really want to put something to the `props`.

I just want to avoid errors such as these:

```
Warning: setState(...): Can only update a mounted or mounting component. This usually means you called setState() on an unmounted component. This is a no-op. Please check the code for the Resolver component.
```

```
Warning: setState(...): Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.
```

Beginne damit, die asynchronen Aktualisierungen der Resolver-Komponente während der react-router-Berechtigungsweiterleitung nachzuverfolgen, und reproduziere beide Warnungen. Erledigt ist die Aufgabe, wenn eine Weiterleitung bei fehlender Anforderung keine der beiden setState-Warnungen mehr erzeugt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.