audio: Clarified SDL_GetAudioStreamQueued docs.

include/SDL3/SDL_audio.h

@@ -1322,6 +1322,12 @@ extern SDL_DECLSPEC int SDLCALL SDL_GetAudioStreamAvailable(SDL_AudioStream *str
 /**
  * Get the number of bytes currently queued.
  *
+ * This is the number of bytes put into a stream as input, not the number
+ * that can be retrieved as output. Because of several details, it's not
+ * possible to calculate one number directly from the other. If you need to
+ * know how much usable data can be retrieved right now, you should use
+ * SDL_GetAudioStreamAvailable() and not this function.
+ *
  * Note that audio streams can change their input format at any time, even if
  * there is still data queued in a different format, so the returned byte
  * count will not necessarily match the number of _sample frames_ available.