Okay, just tried recompiling ZMusic (GZDoom dependency) and it fixed the crash - I'm guessing that this was the fix that went in just today: https://github.com/ZDoom/ZMusic/commit/f6facdaa683e7159b7569d5287a088da352a7c92
So hopefully a GZDoom minor version update will release soon that fixes this for everyone. And if you're compiling your own, you can get it right away.