[BUG?] Music selection in 12.9

[Proxima]

Not sure if there's a bug here or if I've just done something stupid.

I am attempting to split the "Extra Levels" pack into separate packs for 2P, Genesis, and so on. I have moved the level subfolders from Extra into the main levels folder, gone into each pack's levels.nxmi, and added "BASE" at the start to show that it's (now) a separate pack. In case it makes a difference, I've done this on a brand-new installation of 12.9 with no other levels other than Redux installed.

To help reproduce the bug, I've attached a zip with the exact current state of my levels folder.

Expected: Each pack starts the music rotation with track 1 (Cancan).
Observed: NL treats all the packs as if they were a single pack, so 2P ends with track 11, and the next pack starts with track 12.

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On a similar note, it was mentioned on discord the other day that it would be desirable if putting a music.nxmi inside a rank folder told NL "use this music rotation for this rank, and start with track 1". An example use-case that came up was WillLem's Amiga Lemmings project, where he would like to have an overall music rotation for the pack, but restart from track 1 with the 2P rank.

[namida]

Haven't outright tested yet, but a quick look at the code suggests the "which music" code for rotatoin basically falls apart as soon as there's a deviation from "normal" pack structure (it's a bit messy trying to do a "music carries over between ranks" in a setup where a "rank" vs "pack" distinction is very weak in the first place, and nested ranks are allowed, etc). I'll sort this out next time I'm working on coding.

[namida]

Fixed in commit a99736d (including the music.nxmi's for sub-ranks thing).