Protection against multiple AsioOut initializations doesn't work if no waveProvider presented

[vsoldatkin]

As far as I was able to understand an AsioOut instance must be initialized only once, as suggested by this helpful check:

NAudio/NAudio/Wave/WaveOutputs/AsioOut.cs

Lines 193 to 203 in 4bf547f

	public void InitRecordAndPlayback(IWaveProvider waveProvider, int recordChannels, int recordOnlySampleRate)
	{
	if (this.sourceStream != null)
	{
	throw new InvalidOperationException("Already initialised this instance of AsioOut - dispose and create a new one");
	}
	int desiredSampleRate = waveProvider != null ? waveProvider.WaveFormat.SampleRate : recordOnlySampleRate;
	if (waveProvider != null)
	{
	sourceStream = waveProvider;

public void InitRecordAndPlayback(IWaveProvider waveProvider, int recordChannels, int recordOnlySampleRate)
{
    if (this.sourceStream != null)
    {
        throw new InvalidOperationException("Already initialised this instance of AsioOut - dispose and create a new one");
    }
  
...

    if (waveProvider != null)
    {
        sourceStream = waveProvider;
...
    }

The problem though is that this check doesn't work well when no waveProvider was initialy provided (as for recording only application) and sourceStream is always null. Seems like a boolean flag might be a better idea.