Construct 3 r406.2

Notes

A potentially serious issue with our new support for lossy spritesheets came up. As we're close to a stable release, out of an abundance of caution we're releasing the fix early to make sure we're confident it works correctly. If all is well, we may still be able to proceed with a stable release next week, but note as ever if anything serious comes up before then there may still be a delay. Happy testing!