Bug Report: Custom difficulty sprites don't show up in freeplay

[MAZ12211]

Issue Checklist

• I have properly named my issue
• I have checked the Issues/Discussions pages to see if my issue has already been reported

Platform

Itch.io (Downloadable Build) - Windows

Browser

None

Version

0.5.3

Description (include any images, videos, errors, or crash logs)

If you have a custom difficulty called let's say Mania, it wouldn't show up in free play (or it shows up but invisible) even though the chart and the metadata has the required information
The difficulty is still playable but the sprite is invisible for some reason

This wasn't an issue with previous versions

Steps to Reproduce

1. Make a custom chart with a custom difficulty (not a variation!)
2. Have the image asset for it ready and place it in images/freeplay