mixer_sound fix x64 build issue
Fixes this compile error in x64:
sdl/mixer_sound.c: In function ‘I_SongPlaying’:
sdl/mixer_sound.c:553:3: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
(boolean)music
^
Fixes this compile error in x64:
sdl/mixer_sound.c: In function ‘I_SongPlaying’:
sdl/mixer_sound.c:553:3: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
(boolean)music
^