extracting .iso files in parallel with small batch size fails

[svenclaesson]

This test fails

        [DataRow("TestData.iso")]
        public void ExtractArchiveSmallBatchSize(string fileName, int expectedNumFiles = 3)
        {
            var extractor = new Extractor();
            var path = Path.Combine(Directory.GetCurrentDirectory(), "TestData", "TestDataArchives", fileName);
            var results = extractor.Extract(path, new ExtractorOptions() { Parallel = true, BatchSize = 2 });
            Assert.AreEqual(expectedNumFiles, results.Count(entry => entry.EntryStatus == FileEntryStatus.Default));
        }