fixing macOS sound crash

make sure no completion call gets triggered after this point

src/osx/core/sound.cpp

@@ -94,6 +94,7 @@ void wxOSXAudioToolboxSoundData::DoStop()
     if ( m_playing )
     {
         m_playing = false;
+        AudioServicesRemoveSystemSoundCompletion(m_soundID);
         AudioServicesDisposeSystemSoundID (m_soundID);
 
         wxSound::SoundStopped(this);