Add unit tests for layout/get_min_size/draw methods

Some views _need_ some minimal space to display properly. It's usually just a few cells, but as views include other views, it adds up. And while it's rarely an issue in regular use, when resizing a view, it can happen, if only temporarily.

Currently, it often results in a panic from usize overflows.

Rather than crashing, displaying an empty view would be a minimal thing to do. Showing an error message (like "Screen size too small" or something) would be even better.