fix JailAudioSDL3: havia un error de copy-paste

source/external/jail_audio.cpp

@@ -487,7 +487,7 @@ void JA_StopChannel(const int channel)
         {
             if (channels[i].state != JA_CHANNEL_FREE)
                 SDL_DestroyAudioStream(channels[i].stream);
-            channels[channel].stream = nullptr;
+            channels[i].stream = nullptr;
             channels[i].state = JA_CHANNEL_FREE;
             channels[i].pos = 0;
             channels[i].sound = NULL;