According to http://www.libsdl.org/projects/SDL_mixer/docs/SDL_mixer.pdf, 0 is the only value for the loop argument that does not cause looping on Mix_PlayMusic. Update Emscripten's implementation to respect this.
Make looping behavior on effects match background music.
Merge pull request #1199 from j4m3z0r/sdl-fixes

Fix Mix_PlayMusic's handling of loop argument in SDL