Adding new MarkerManager removes an old one

[antjkennedy]

When adding new MarkerManagers (in AbstractMapDisplay) before any markers have been added anywhere in an Unfolding application the first entry is always removed. See below

public void addMarkerManager(MarkerManager<Marker> markerManager) {
        // Replace default MarkerManager, if only default exists and has no entries
        if (markerManagerList.size() == 1 && markerManagerList.get(0).getMarkers().size() == 0) {
            markerManagerList.remove(0);
        }

        markerManagerList.add(markerManager);
    }

Prehaps this could change to

public void addMarkerManager(MarkerManager<Marker> markerManager) {
        // Replace default MarkerManager, if only default exists and has no entries
        if (markerManagerList.size() == 1) {
            MarkerManager<?> mm = markerManagerList.get(0);
            if (mm.getMarkers().size() == 0 && mm.equals(this.defaultMarkerManager)) {
                markerManagerList.remove(0);
            }
        }

        markerManagerList.add(markerManager);
    }