v0.5.1

Small fix to progressive rendering.

What's Changed

• Fix progressive rendering previews for progressive-dc=2 images by @veluca93 in #837
• Replace some as pointer casts with .cast::<T>(). by @veluca93 in #838
• v0.5.1 by @veluca93 in #839

Full Changelog: v0.5.0...v0.5.1