SDL_LoadWAV_IO(): On error, set *audio_buf to NULL and *audio_len to 0

(cherry picked from commit 23e08f7807)

src/audio/SDL_wave.c

@@ -2114,8 +2114,8 @@ bool SDL_LoadWAV_IO(SDL_IOStream *src, bool closeio, SDL_AudioSpec *spec, Uint8
     result = WaveLoad(src, &file, spec, audio_buf, audio_len);
     if (!result) {
         SDL_free(*audio_buf);
-        audio_buf = NULL;
-        audio_len = 0;
+        *audio_buf = NULL;
+        *audio_len = 0;
     }
 
     // Cleanup