Menu music not playing when returning to menu

[verhoevenv]

I suspect the intention was to make the menu music play whenever the menu is shown, however there's a bug in that code: at https://github.com/verhoevenv/OpenNotrium/blob/96bad237cbbc4f162bd7e45dc9866934768385fa/WinMain.cpp#L1340

SwapSourceFilter("music/menu/menu.mp3");

references an unknown file, it should be

SwapSourceFilter("music/menu.mp3");

[Enet4]

I would prefer moving any hard-coded file names like those into a single place. And the fact that we're calling a function called "SwapSourceFilter" in the main file doesn't comfort me either. :P