cached_network_image_sandbox

Minimal repro case for Baseflow/flutter_cached_network_image#527

When an image can't be loaded for any reason (404, wrong format, ...), an unhandled exception is thrown, unless errorWidget is used.

However, when pushing a new route, the unhandled exception is thrown anyway for each image in error on the current route, even when using errorWidget. This is annoying both in dev (lots of logs) and in prod (Crahslytics is flooded by those errors).