Investigate reason for cut sound with QSoundEffect on Windows

The qml-minimal-sound-effect manual test plays a sound that should have two distinct peaks, like two drops hitting the water. When played on Windows, only one is heard, even with environment variable QT_DISABLE_AUDIO_PREPARE=0

Note that when adding a Sleep(500) before releasing the m_audioClient in QWindowsAudioSink::close() fixes the problem, even with QT_DISABLE_AUDIO_PREPARE=1. This might indicate that the IAudioClient interface is released before it is finished playing.

See sequence diagram for the setup of QSoundEffect with the qml-minimal-sound-effect manual test, where releasing the IAudioClient interface happens at the very bottom.