docs: warn not to destroy an SDL_AudioStream during its callback.

Fixes #15871.

include/SDL3/SDL_audio.h

@@ -1854,6 +1854,8 @@ extern SDL_DECLSPEC bool SDLCALL SDL_UnlockAudioStream(SDL_AudioStream *stream);
  * appropriate, but the system goes on with the data currently available to it
  * if this callback does nothing.
  *
+ * Do not call SDL_DestroyAudioStream() on `stream` during this callback.
+ *
  * \param stream the SDL audio stream associated with this callback.
  * \param additional_amount the amount of data, in bytes, that is needed right
  *                          now.