[raudio]: free converterResidual in UnloadSoundAlias to prevent leak

The example audio_sound_multi was leaking memory every single time the spacebar was pressed.

```c
Direct leak of 576 byte(s) in 9 object(s) allocated from:
    #0 0x758a41019447 in calloc (/usr/lib/liblsan.so.0+0x19447) (BuildId: 8ee115309adc591d231c961c43d245cfa68d9aa7)
    #1 0x562dfbd2c4f3 in LoadAudioBuffer (/home/peter/raylib/examples/audio/audio_sound_multi+0xfa4f3) (BuildId: ea2a6f45d724abeccf904143a32012266f259f93)
```

This patch fixes that leak.

src/raudio.c

@@ -1048,6 +1048,7 @@ void UnloadSoundAlias(Sound alias)
     {
         UntrackAudioBuffer(alias.stream.buffer);
         ma_data_converter_uninit(&alias.stream.buffer->converter, NULL);
+        RL_FREE(alias.stream.buffer->converterResidual);
         RL_FREE(alias.stream.buffer);
     }
 }