Fixes scenario wherein entering the first run setup overlay, exiting at
the "UI scale" step (which shows a song select), then moving to actua
song select and trying to select a mod would lead to a crash.
The crash was caused by two active mod screen instances attempting to
swap the global mod bindable's mod instances for ones they owned. This
logic - while generally problematic and hard to maintain - was fixing
several issues with mod reference management and setting copying, so I'm
letting it live another day.
This change will mean that the song select preview on the "UI scale"
step will not receive the same mods that the actual game has enabled.
That said, it already doesn't use the same beatmap or ruleset, so this
looks fine to break.
