audio: Add NULL check to SDL_UnbindAudioStreams

include/SDL3/SDL_audio.h

@@ -990,7 +990,7 @@ extern SDL_DECLSPEC bool SDLCALL SDL_BindAudioStream(SDL_AudioDeviceID devid, SD
  *
  * Unbinding a stream that isn't bound to a device is a legal no-op.
  *
- * \param streams an array of audio streams to unbind.
+ * \param streams an array of audio streams to unbind. Can be NULL or contain NULL.
  * \param num_streams number streams listed in the `streams` array.
  *
  * \threadsafety It is safe to call this function from any thread.
@@ -1007,7 +1007,7 @@ extern SDL_DECLSPEC void SDLCALL SDL_UnbindAudioStreams(SDL_AudioStream * const
  * This is a convenience function, equivalent to calling
  * `SDL_UnbindAudioStreams(&stream, 1)`.
  *
- * \param stream an audio stream to unbind from a device.
+ * \param stream an audio stream to unbind from a device. Can be NULL.
  *
  * \threadsafety It is safe to call this function from any thread.
  *

src/audio/SDL_audio.c

@@ -1949,6 +1949,10 @@ bool SDL_BindAudioStream(SDL_AudioDeviceID devid, SDL_AudioStream *stream)
 // !!! FIXME: this and BindAudioStreams are mutex nightmares.  :/
 void SDL_UnbindAudioStreams(SDL_AudioStream * const *streams, int num_streams)
 {
+    if (num_streams <= 0 || !streams) {
+        return; // nothing to do
+    }
+
     /* to prevent deadlock when holding both locks, we _must_ lock the device first, and the stream second, as that is the order the audio thread will do it.
        But this means we have an unlikely, pathological case where a stream could change its binding between when we lookup its bound device and when we lock everything,
        so we double-check here. */