Rare thread race crashes on song load/save

[8bitbubsy]

Still a bit unclear what is really causing this (except for my poor threading code), but I have gotten a few crash reports from a couple of people. The crash on load seems related to some thread race condition in setupLoadedModule().

[8bitbubsy]

TODO to self: Create fuzzing code in debug mode that attempts to spam-save a playing module in a separate thread? Be sure to force-disable overwrite warning.