Detect if internet isn't available

While using `django-geoposition` in my Django project together with the [`suit`](http://djangosuit.com/) admin theme, I noticed that while working in the admin and not connected to the internet (e.g., running `manage.py runserver` locally) none of my fields would render properly on the pages that use `suit`'s tab features.

I realized that the reason for that was that `geoposition`'s javascript would try to load the Google Maps JS, and it would fail since the Google Maps API hadn't loaded, and that would stop all of the rest of the JS from running, including `suit`'s JS.

I've added a `try/catch` to detect the `ReferenceError` for `google` in the javascript so that the rest of the Javascript on the page can continue to run in that scenario.