Display which paths led to "Illegal BMS Songs" error

[Chazoshtare]

Currently, if a user would have any illegal BMS files or the detection system would react on any false positives, there is no way to tell which BMS files cause the error.

This PR adds paths to the error message displayed, so it's easier for the user to identify which song packs should be deleted or included in an issue about false positives.

The paths displayed are capped at 30 lines to limit the dialog window potential size.

---

Detected charts are not stored in a variable in MainLoader anymore, and two unreachable checks were also removed - they cannot happen if the application won't start anyway.

Part of this PR just removes unneeded whitespace, but it's split in separate commits. Main commit that represents the main logic change can be viewed here: https://github.com/exch-bms2/beatoraja/pull/631/commits/3517fc0a80dd4f72d71f6af159be539709579ba7