public Completable waitForEndCompletable(@Nullable final DisposableHandler handler) {
        if (handler != null) {
            handler.add(disposable);
        }
        loading.onComplete();
        return waitForEnd;
    }
Caches are loaded from disk on a computation scheduler to avoid using more threads than cores while decoding
the image. Downloads happen on downloadScheduler, in parallel with image decoding.
main/src/main/java/cgeo/geocaching/network/HtmlImage.java