Unhandled IOException when trying to cancel operation and the ffmpeg process has already exited

[snechaev]

We have registered the cancellationToken in the ProcessExtensions.WaitForExitAsync() . The registered cancellation handler attempts to write some data to the process's stdin.

If the process has already exited, there is a try/catch block exists which ignores the InvalidOperationException.

FFmpeg.NET/src/FFmpeg.NET/Extensions/ProcessExtensions.cs

Lines 20 to 33 in 16fe394

	try
	{
	if (stdInDataInput)
	// If standard input used for data input just close it.
	// It will force process to stop (closing files).
	process.StandardInput.Close();
	else
	// Send "q" to ffmpeg, which will force it to stop (closing files).
	process.StandardInput.Write("q");
	}
	catch (InvalidOperationException)
	{
	// If the process doesn't exist anymore, ignore it.
	}

However, theStreamWriter.Write() will throw an IOException here when attempting to write q to the stdin of a non-existent process. Therefore, it seems like that we also need to handle the IOException here.