Fix C23 empty initializer warning.

src/audio/alsa/SDL_alsa_audio.c

@@ -497,6 +497,7 @@ struct ALSA_pcm_cfg_ctx {
 static enum snd_pcm_chmap_position sdl_channel_maps[SDL_AUDIO_ALSA__SDL_CHMAPS_N][SDL_AUDIO_ALSA__CHMAP_CHANS_N_MAX] = {
     // 0 channels
     {
+        0
     },
     // 1 channel
     {