Fix audio leaking in builtin SDL_mixer

Author: caiiiycuk

src/library_sdl.js

@@ -2817,6 +2817,7 @@ var LibrarySDL = {
   Mix_ReserveChannels: (num) => {
     SDL.channelMinimumNumber = num;
   },
+  Mix_PlayChannelTimed__deps: ['Mix_HaltChannel'],
   Mix_PlayChannelTimed__proxy: 'sync',
   Mix_PlayChannelTimed: (channel, id, loops, ticks) => {
     // TODO: handle fixed amount of N loops. Currently loops either 0 or infinite times.
@@ -2863,6 +2864,9 @@ var LibrarySDL = {
       if (channelInfo.audio == this) { channelInfo.audio.paused = true; channelInfo.audio = null; }
       if (SDL.channelFinished)  {{{ makeDynCall('vi', 'SDL.channelFinished') }}}(channel);
     }
+    if (channelInfo.audio) {
+      _Mix_HaltChannel(channel);
+    }
     channelInfo.audio = audio;
     // TODO: handle N loops. Behavior matches Mix_PlayMusic
     audio.loop = loops != 0;