[TIMOB-25487] Android: Prevent kroll from removing null proxy object pointer

[garymathews]

• There is no null object reference check when removing a proxy object pointer, causing a crash on garbage collection

TEST CASE

• Repeatedly view and back-out from the map until crash
• This will be re-producible in other cases, but can consistently be reproduced with ti.map due to its heavy memory usage

var MapModule = require('ti.map'),
    win = Titanium.UI.createWindow({backgroundColor: 'gray'}),
    btn = Ti.UI.createButton({title: 'VIEW MAP'});

function viewMap () {
    var win = Ti.UI.createWindow({backgroundColor: 'gray'}),
        mapView = MapModule.createView({
            userLocation: true,
            mapType: MapModule.NORMAL_TYPE,
            animate: true,
            region: {latitude: -33.87365, longitude: 151.20689, latitudeDelta: 0.1, longitudeDelta: 0.1 }
        });
    win.add(mapView);
    win.open();
}

btn.addEventListener('click', function (e) {
	if (Ti.Geolocation.hasLocationPermissions()) {
        viewMap();
    } else {
        Ti.Geolocation.requestLocationPermissions(function (e) {
            if (e.success === true) {
                viewMap();
            } else {
                alert('permissions denied: ' + e.error);
            }
        });
	}
});

win.add(btn);
win.open();

JIRA Ticket