update for new thread-safe environment functions in SDL3

Closes: #633

Author: sezero

examples/playmus.c

@@ -205,7 +205,7 @@ int main(int argc, char *argv[])
     Mix_VolumeMusic(audio_volume);
 
     /* Set the external music player, if any */
-    Mix_SetMusicCMD(SDL_getenv("MUSIC_CMD"));
+    Mix_SetMusicCMD(SDL_GetEnvironmentVariable(SDL_GetEnvironment(), "MUSIC_CMD"));
 
     while (argv[i]) {
         next_track = 0;

src/codecs/music_timidity.c

@@ -59,7 +59,7 @@ static int TIMIDITY_Open(const SDL_AudioSpec *spec)
 
     (void) spec;
 
-    cfg = SDL_getenv("TIMIDITY_CFG");
+    cfg = SDL_GetEnvironmentVariable(SDL_GetEnvironment(), "TIMIDITY_CFG");
     if(!cfg) cfg = Mix_GetTimidityCfg();
     if (cfg) {
         return Timidity_Init(cfg); /* env or user override: no other tries */

src/effects_internal.c

@@ -37,7 +37,7 @@ int _Mix_effects_max_speed = 0;
 
 void _Mix_InitEffects(void)
 {
-    _Mix_effects_max_speed = (SDL_getenv(MIX_EFFECTSMAXSPEED) != NULL);
+    _Mix_effects_max_speed = (SDL_GetEnvironmentVariable(SDL_GetEnvironment(), MIX_EFFECTSMAXSPEED) != NULL);
 }
 
 void _Mix_DeinitEffects(void)

src/music.c

@@ -1495,7 +1495,7 @@ SDL_bool Mix_SetSoundFonts(const char *paths)
 
 const char* Mix_GetSoundFonts(void)
 {
-    const char *env_paths = SDL_getenv("SDL_SOUNDFONTS");
+    const char *env_paths = SDL_GetEnvironmentVariable(SDL_GetEnvironment(), "SDL_SOUNDFONTS");
     SDL_bool force_env_paths = SDL_GetHintBoolean("SDL_FORCE_SOUNDFONTS", SDL_FALSE);
     if (force_env_paths && (!env_paths || !*env_paths)) {
         force_env_paths = SDL_FALSE;