Fix songs not ending in rare cases, take 2

[TheNathannator]

Let's try this again, shall we?

From the original PR:

Some songs (presumably with corrupt audio files) have reported lengths longer than BASS can play. Therefore the song's position never reached the supposed length and the gameplay never ended.

Instead of using the song position, it now uses SYNC events in BASS with callbacks. Probably not done in the nicest way but it did work in quick testing.

I have verified that the song that had issues reported ends correctly, and that other songs (including both .ini and CON songs) also end correctly.