It turns out that it should be initialized after Mixer class (SDL_mixer docs say so,
however official examples use it the other way around. But also it doesn't seem to
ne necessary at all, as SDL loads needed libraries automatically anyway
Though these are broken and error prone, as they ignore the possibility
of conflicts between SDL, SDL2 and wrappers thereof discarding useful
include path prefix (SDL2/), since SDL and satellite libraries follow
these it's too hard to stay away.
So don't use prefixes for SDL include paths any longer.